Initial success

2 files changed, 2693 insertions, 0 deletions

diff --git a/src/vm/de/mod.rs b/src/vm/de/mod.rs
new file mode 100644
index 0000000..3cba18a
--- /dev/null
+++ b/src/vm/de/mod.rs
@@ -0,0 +1,2175 @@
+// Copyright (C) 2022 Soni L.
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+//! Deserialization-related parts of the VM.
+
+use std::borrow::Cow;
+use std::marker::PhantomData;
+
+use indexmap::IndexMap;
+
+use serde::Serialize;
+use serde::de::Error as _;
+use serde::de::IntoDeserializer as _;
+
+use smallvec::SmallVec;
+
+use super::Frame;
+use super::Interpreter;
+use super::Pack;
+use super::PatternConstants;
+use super::PatternElement;
+use super::SerdeObject;
+use super::Type;
+use super::Value;
+use crate::errors::MatchError;
+use crate::errors::QueryError;
+
+mod unpacker;
+
+pub use unpacker::Unpacker;
+
+/// A `DeserializeSeed` for Datafu input.
+///
+/// This converts from Serde to Datafu's internal representation (a "pack").
+pub(crate) struct Packer<'pat, 'state, O: Serialize> {
+    /// The global interpreter state.
+    interp: Interpreter<'pat, 'state, O>,
+    /// Current call limit.
+    call_limit: usize,
+    /// Whether we're collecting values.
+    collecting: bool,
+}
+
+struct FramesMut<'packer, 'pat> {
+    frames: &'packer mut Vec<Frame<'pat>>,
+}
+
+struct Frames<'packer, 'pat> {
+    frames: &'packer Vec<Frame<'pat>>,
+}
+
+impl<'packer, 'pat> FramesMut<'packer, 'pat> {
+    fn iter_mut<'a>(
+        &'a mut self,
+    ) -> impl Iterator<Item=&'a mut Frame<'pat>> + DoubleEndedIterator
+    where
+        'packer: 'a,
+    {
+        self.frames.iter_mut()
+    }
+
+    fn iter_active_mut<'a>(
+        &'a mut self,
+    ) -> impl Iterator<Item=&'a mut Frame<'pat>> + DoubleEndedIterator
+    where
+        'packer: 'a,
+    {
+        self.iter_mut().filter(|frame| {
+            frame.active()
+        })
+    }
+}
+
+impl<'packer, 'pat> Frames<'packer, 'pat> {
+    fn iter<'a>(
+        &'a self,
+    ) -> impl Iterator<Item=&'a Frame<'pat>> + DoubleEndedIterator
+    where
+        'packer: 'a,
+    {
+        self.frames.iter()
+    }
+
+    fn iter_active<'a>(
+        &'a self,
+    ) -> impl Iterator<Item=&'a Frame<'pat>> + DoubleEndedIterator
+    where
+        'packer: 'a,
+    {
+        self.iter().filter(|frame| {
+            frame.active()
+        })
+    }
+}
+
+impl<'pat, 'state, 'de, O: Serialize> Packer<'pat, 'state, O> {
+    /// Creates a new Packer.
+    pub(crate) fn new(
+        interp: Interpreter<'pat, 'state, O>,
+        call_limit: usize,
+    ) -> Self {
+        Self {
+            interp: interp,
+            call_limit: call_limit,
+            collecting: false,
+        }
+    }
+
+    fn frames_mut(&mut self) -> FramesMut<'_, 'pat> {
+        FramesMut {
+            frames: &mut *self.interp.frames,
+        }
+    }
+
+    fn frames(&mut self) -> Frames<'_, 'pat> {
+        Frames {
+            frames: &*self.interp.frames,
+        }
+    }
+
+    /// Steps the VM into the next operation.
+    fn step_in<E: serde::de::Error>(&mut self) -> Result<(), E> {
+        if self.call_limit > 0 {
+            self.call_limit -= 1;
+        } else {
+            self.interp.error.insert(MatchError::StackOverflow);
+            return Err(E::custom("stack overflow"));
+        }
+        // iterate up to the *live* length (i.e. the loop is allowed to modify
+        // the length).
+        // NOTE: we need to use while-let so as to not borrow anything in an
+        // iterator. filtering happens on the *result* of the iterator.
+        let mut index_iter = 0..;
+        while let Some(index) = index_iter.next().filter(|&i| {
+            i < self.interp.frames.len()
+        }) {
+            let frame = &mut self.interp.frames[index];
+            if frame.overstep > 0 || !frame.matches {
+                // overstepped and non-matching frames
+                frame.overstep += 1;
+                // FIXME check if this is correct (it probably isn't)
+                //frame.matches = false;
+            } else {
+                if !frame.next() {
+                    // empty/end-of frames
+                    // 1 layer of step-in.
+                    // step-out will undo this.
+                    // this is correct because this branch implies overstep = 0
+                    frame.overstep = 1;
+                    // FIXME we still don't think this is correct
+                    frame.matches = false;
+                } else if matches!(
+                    frame.op(),
+                    PatternElement::SubtreeMarker,
+                ) {
+                    // subtrees!
+                    // these are tricky, because the current frame can be moved
+                    // in memory. so we have to use indexing every time.
+                    // tho first we set it as overstep because it has special
+                    // handling.
+                    frame.overstep = 1;
+                    frame.matches = false;
+                    let mut at = index + 1;
+                    while self.interp.frames[index].next() {
+                        let op = self.interp.frames[index].raw_op();
+                        if let PatternElement::ValueSubtree {
+                            index: subtree, ..
+                        } = op {
+                            let new_frame = Frame {
+                                ops: &self.interp.pat.protos[subtree][..],
+                                iar: None,
+                                overstep: 0,
+                                matches: true,
+                                poison: false,
+                            };
+                            debug_assert!(!new_frame.ops.is_empty());
+                            // we want the "newest" frame last, so it is
+                            // easier to unwind back.
+                            self.interp.frames.insert(at, new_frame);
+                            at += 1;
+                        } else {
+                            unreachable!()
+                        }
+                    }
+                }
+            }
+        }
+        Ok(())
+    }
+
+    /// Steps the VM back into the previous operation.
+    fn step_out<E: serde::de::Error>(
+        &mut self,
+        mut packs: Vec<Pack<'pat, 'de>>,
+    ) -> Result<Vec<Pack<'pat, 'de>>, E> {
+        // this code attempts to maintain the logical invariant of:
+        // self.frames().iter_active().count() == packs.len()
+        self.call_limit += 1;
+        let mut index_iter = 0..;
+        let mut pack_index = packs.len();
+        let orig_len = self.interp.frames.len();
+        while let Some(index) = index_iter.next().filter(|&i| {
+            i < orig_len
+        }) {
+            // iterate backwards
+            let index = orig_len - index - 1;
+            let frame = &mut self.interp.frames[index];
+            let mut has_pack = frame.matches;
+            if frame.overstep > 0 {
+                // handle overstep
+                frame.overstep -= 1;
+            } else {
+                if has_pack {
+                    pack_index -= 1;
+                }
+                if frame.poison {
+                    // FIXME should frame.poison always remove the pack?
+                    if frame.is_value() {
+                        if has_pack {
+                            packs.remove(pack_index);
+                        }
+                        frame.matches = false;
+                        has_pack = false;
+                        frame.poison = false;
+                    }
+                }
+                // unwind frame
+                if frame.prev() {
+                    // successfully unwound. do nothing.
+                } else {
+                    // find parent frame.
+                    let mut count = 1;
+                    let mut target = index;
+                    let mut target_pack = pack_index;
+                    while count > 0 && target > 0 {
+                        target -= 1;
+                        if self.interp.frames[target].matches {
+                            debug_assert!(target_pack > 0);
+                            target_pack -= 1;
+                        }
+                        match self.interp.frames[target].num_subtrees() {
+                            Some((num, _)) if num < count => {
+                                count -= num;
+                            },
+                            Some((num, _)) => {
+                                count = 0;
+                            },
+                            None => {
+                                count += 1;
+                            },
+                        }
+                    }
+                    if count == 0 {
+                        // found target frame
+                        let frame = self.interp.frames.remove(index);
+                        let target_frame = &mut self.interp.frames[target];
+                        let (_, optional) = target_frame.value_subtree();
+                        target_frame.prev().then(|| ()).unwrap();
+                        if has_pack {
+                            let pack = packs.remove(pack_index);
+                            if !target_frame.matches {
+                                packs.insert(target_pack, pack);
+                                target_frame.matches = true;
+                                pack_index += 1;
+                            } else {
+                                packs[target_pack].zip(pack);
+                            }
+                        } else {
+                            //if frame.poison {
+                            //    target_frame.poison = true;
+                            //}
+                            if !optional {
+                                self.interp.error.insert({
+                                    MatchError::ValidationError
+                                });
+                                return Err(E::custom("subtree failed"));
+                            }
+                        }
+                        if let Some((0, _)) = target_frame.num_subtrees() {
+                            target_frame.overstep = 0;
+                        }
+                    }
+                }
+            }
+        }
+        Ok(packs)
+    }
+}
+
+impl<'pat, 'state, 'de, O> serde::de::DeserializeSeed<'de>
+for &mut Packer<'pat, 'state, O>
+where
+    O: Serialize,
+{
+    type Value = (Vec<Pack<'pat, 'de>>, Option<SerdeObject<'de>>);
+    fn deserialize<D>(
+        mut self,
+        deserializer: D,
+    ) -> Result<Self::Value, D::Error>
+    where
+        D: serde::Deserializer<'de>
+    {
+        if let Err(e) = self.step_in() { return Err(e); }
+        let pat = self.interp.pat;
+        let target_type = self.frames().iter_active().try_fold(
+            Type::IgnoredAny,
+            |target_type, frame| {
+                Ok(match (target_type, frame.get_type()) {
+                    // required type binds stronger than any/ignored_any
+                    (Type::IgnoredAny, Some((ty, true))) => ty,
+                    (Type::Any, Some((ty, true))) => ty,
+                    // and also stronger than optional any/ignored_any
+                    (ty, Some((Type::IgnoredAny, _))) => ty,
+                    (ty, Some((Type::Any, _))) => ty,
+                    // None effectively falls back into any
+                    (Type::IgnoredAny, None) => Type::Any,
+                    (ty, None) => ty,
+                    // prefer owned if any branch prefers owned
+                    (Type::String, Some((Type::Str, true))) => {
+                        Type::String
+                    },
+                    (Type::Str, Some((Type::String, true))) => {
+                        Type::String
+                    },
+                    (Type::Bytes, Some((Type::ByteBuf, true))) => {
+                        Type::ByteBuf
+                    },
+                    (Type::ByteBuf, Some((Type::Bytes, true))) => {
+                        Type::ByteBuf
+                    },
+                    // types which are the same are okay
+                    (left, Some((right, _))) if left == right => {
+                        left
+                    },
+                    // optional type vs Any/IgnoredAny prefers Any
+                    (Type::IgnoredAny, Some((_, false))) => Type::Any,
+                    (Type::Any, Some((_, false))) => Type::Any,
+                    // types which are not the same are an error because we
+                    // only request a specific type if it's actually required
+                    (left, Some((right, _))) => {
+                        return Err(MatchError::Unsatisfiable);
+                    },
+                })
+            },
+        );
+        let target_type = match target_type {
+            Ok(target_type) => target_type,
+            Err(e) => {
+                self.interp.error.insert(e);
+                return Err(D::Error::custom("type conflict"));
+            },
+        };
+        match target_type {
+            Type::Any => deserializer.deserialize_any(&mut *self),
+            Type::IgnoredAny => {
+                deserializer.deserialize_ignored_any(&mut *self)
+            },
+            Type::Bool => deserializer.deserialize_bool(&mut *self),
+            Type::I8 => deserializer.deserialize_i8(&mut *self),
+            Type::I16 => deserializer.deserialize_i16(&mut *self),
+            Type::I32 => deserializer.deserialize_i32(&mut *self),
+            Type::I64 => deserializer.deserialize_i64(&mut *self),
+            Type::I128 => deserializer.deserialize_i128(&mut *self),
+            Type::U8 => deserializer.deserialize_u8(&mut *self),
+            Type::U16 => deserializer.deserialize_u16(&mut *self),
+            Type::U32 => deserializer.deserialize_u32(&mut *self),
+            Type::U64 => deserializer.deserialize_u64(&mut *self),
+            Type::U128 => deserializer.deserialize_u128(&mut *self),
+            Type::F32 => deserializer.deserialize_f32(&mut *self),
+            Type::F64 => deserializer.deserialize_f64(&mut *self),
+            Type::Char => deserializer.deserialize_char(&mut *self),
+            Type::Str if !self.collecting => {
+                deserializer.deserialize_str(&mut *self)
+            },
+            Type::Str | Type::String => {
+                deserializer.deserialize_string(&mut *self)
+            },
+            Type::Bytes if !self.collecting => {
+                deserializer.deserialize_bytes(&mut *self)
+            },
+            Type::Bytes | Type::ByteBuf => {
+                deserializer.deserialize_byte_buf(&mut *self)
+            },
+            Type::Option => deserializer.deserialize_option(&mut *self),
+            Type::Unit => deserializer.deserialize_unit(&mut *self),
+            Type::Seq => deserializer.deserialize_seq(&mut *self),
+            Type::Map => deserializer.deserialize_map(&mut *self),
+            Type::Identifier => {
+                deserializer.deserialize_identifier(&mut *self)
+            },
+            Type::Tuple(len) => {
+                deserializer.deserialize_tuple(len, &mut *self)
+            },
+            Type::UnitStruct(name) => {
+                deserializer.deserialize_unit_struct(name, &mut *self)
+            },
+            Type::NewtypeStruct(name) => {
+                deserializer.deserialize_newtype_struct(name, &mut *self)
+            },
+            Type::TupleStruct { name, len } => {
+                deserializer.deserialize_tuple_struct(name, len, &mut *self)
+            },
+            Type::Struct { name, fields } => {
+                deserializer.deserialize_struct(name, fields, &mut *self)
+            },
+            Type::Enum { name, variants } => {
+                deserializer.deserialize_enum(name, variants, &mut *self)
+            },
+        }.and_then(|(packs, obj)| Ok((self.step_out(packs)?, obj)))
+    }
+}
+
+/// visit method generator for simple values (primitives).
+///
+/// can generate whole function or just the glue.
+macro_rules! vs {
+    (fn $visit:ident $obj:ident ($data_type:pat) $rust_type:ty) => {
+        fn $visit<E>(mut self, v: $rust_type) -> Result<Self::Value, E>
+        where
+            E: serde::de::Error,
+        {
+            vs!(self (v) $obj ($data_type))
+        }
+    };
+    ($this:ident $v:tt $obj:ident ($data_type:pat)) => {
+        {
+            let pat = $this.interp.pat;
+            let mut obj = None;
+            if $this.collecting {
+                obj = Some(SerdeObject::$obj$v);
+            }
+            let mut packs = Vec::new();
+            let result = {
+                $this.frames_mut().iter_active_mut().try_for_each(|frame| {
+                    let ty = frame.get_type();
+                    match ty {
+                        | Some(($data_type, _))
+                        | Some((Type::Any, _))
+                        | Some((Type::IgnoredAny, _))
+                        | None
+                        => {},
+                        Some((_, false)) => {
+                            frame.matches = false;
+                            return Ok(());
+                        },
+                        Some((_, true)) => {
+                            return Err(MatchError::ValidationError)
+                        },
+                    }
+                    let mut pack = Pack::default();
+                    if let Some(name) = frame.get_name(pat) {
+                        let mut map = IndexMap::new();
+                        map.insert(name, SerdeObject::$obj$v);
+                        pack.subpacks.push_back((map, Pack::default()));
+                    }
+                    packs.push(pack);
+                    Ok(())
+                })
+            };
+            match result {
+                Err(e) => {
+                    $this.interp.error.insert(e);
+                    return Err(serde::de::Error::custom("type mismatch"));
+                },
+                _ => (),
+            }
+            Ok((packs, obj))
+        }
+    };
+}
+
+impl<'pat, 'state, 'de, O> serde::de::Visitor<'de>
+for &mut Packer<'pat, 'state, O>
+where
+    O: Serialize,
+{
+    type Value = (Vec<Pack<'pat, 'de>>, Option<SerdeObject<'de>>);
+    fn expecting(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "unsure")
+    }
+
+    vs!(fn visit_bool Bool (Type::Bool) bool);
+    vs!(fn visit_i8 I8 (Type::I8) i8);
+    vs!(fn visit_i16 I16 (Type::I16) i16);
+    vs!(fn visit_i32 I32 (Type::I32) i32);
+    vs!(fn visit_i64 I64 (Type::I64) i64);
+    vs!(fn visit_i128 I128 (Type::I128) i128);
+    vs!(fn visit_u8 U8 (Type::U8) u8);
+    vs!(fn visit_u16 U16 (Type::U16) u16);
+    vs!(fn visit_u32 U32 (Type::U32) u32);
+    vs!(fn visit_u64 U64 (Type::U64) u64);
+    vs!(fn visit_u128 U128 (Type::U128) u128);
+    vs!(fn visit_f32 F32 (Type::F32) f32);
+    vs!(fn visit_f64 F64 (Type::F64) f64);
+    vs!(fn visit_char Char (Type::Char) char);
+
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        let pat = self.interp.pat;
+        let mut obj = None;
+        if self.collecting {
+            obj = Some(SerdeObject::Str(Cow::Owned(v.into())));
+        }
+        let mut packs = Vec::new();
+        let result = {
+            self.frames_mut().iter_active_mut().try_for_each(|frame| {
+                let ty = frame.get_type();
+                match ty {
+                    | Some((Type::String, _))
+                    | Some((Type::Str, _))
+                    | Some((Type::Any, _))
+                    | Some((Type::IgnoredAny, _))
+                    | None
+                    => {},
+                    Some((_, false)) => {
+                        frame.matches = false;
+                        return Ok(());
+                    },
+                    Some((_, true)) => {
+                        return Err(MatchError::ValidationError)
+                    },
+                }
+                match frame.op() {
+                    PatternElement::Value { value: Some(value), .. } => {
+                        match value {
+                            | Value::String { index, skippable }
+                            if pat.strings[index] != v => {
+                                if skippable {
+                                    frame.matches = false;
+                                    return Ok(());
+                                } else {
+                                    return Err(MatchError::ValidationError);
+                                }
+                            },
+                            | Value::Regex { index, skippable }
+                            if !pat.regices[index].is_match(v) => {
+                                if skippable {
+                                    frame.matches = false;
+                                    return Ok(());
+                                } else {
+                                    return Err(MatchError::ValidationError);
+                                }
+                            },
+                            | Value::Type { .. }
+                            | Value::Regex { .. }
+                            | Value::String { .. }
+                            => {}, // ok
+                        }
+                    },
+                    PatternElement::Value { value: None, .. } => {},
+                    _ => unreachable!(),
+                }
+                let mut pack = Pack::default();
+                if let Some(name) = frame.get_name(pat) {
+                    let mut map = IndexMap::new();
+                    map.insert(name, SerdeObject::Str(Cow::Owned(v.into())));
+                    pack.subpacks.push_back((map, Pack::default()));
+                }
+                packs.push(pack);
+                Ok(())
+            })
+        };
+        match result {
+            Err(e) => {
+                self.interp.error.insert(e);
+                return Err(E::custom("type/value mismatch"));
+            },
+            _ => (),
+        }
+        Ok((packs, obj))
+    }
+    fn visit_borrowed_str<E>(self, v: &'de str) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        let pat = self.interp.pat;
+        let mut obj = None;
+        if self.collecting {
+            obj = Some(SerdeObject::Str(Cow::Borrowed(v)));
+        }
+        let mut packs = Vec::new();
+        let result = {
+            self.frames_mut().iter_active_mut().try_for_each(|frame| {
+                let ty = frame.get_type();
+                match ty {
+                    | Some((Type::String, _))
+                    | Some((Type::Str, _))
+                    | Some((Type::Any, _))
+                    | Some((Type::IgnoredAny, _))
+                    | None
+                    => {},
+                    Some((_, false)) => {
+                        frame.matches = false;
+                        return Ok(());
+                    },
+                    Some((_, true)) => {
+                        return Err(MatchError::ValidationError)
+                    },
+                }
+                match frame.op() {
+                    PatternElement::Value { value: Some(value), .. } => {
+                        match value {
+                            | Value::String { index, skippable }
+                            if pat.strings[index] != v => {
+                                if skippable {
+                                    frame.matches = false;
+                                    return Ok(());
+                                } else {
+                                    return Err(MatchError::ValidationError);
+                                }
+                            },
+                            | Value::Regex { index, skippable }
+                            if !pat.regices[index].is_match(v) => {
+                                if skippable {
+                                    frame.matches = false;
+                                    return Ok(());
+                                } else {
+                                    return Err(MatchError::ValidationError);
+                                }
+                            },
+                            | Value::Type { .. }
+                            | Value::Regex { .. }
+                            | Value::String { .. }
+                            => {}, // ok
+                        }
+                    },
+                    PatternElement::Value { value: None, .. } => {},
+                    _ => unreachable!(),
+                }
+                let mut pack = Pack::default();
+                if let Some(name) = frame.get_name(pat) {
+                    let mut map = IndexMap::new();
+                    map.insert(name, SerdeObject::Str(Cow::Borrowed(v)));
+                    pack.subpacks.push_back((map, Pack::default()));
+                }
+                packs.push(pack);
+                Ok(())
+            })
+        };
+        match result {
+            Err(e) => {
+                self.interp.error.insert(e);
+                return Err(E::custom("type/value mismatch"));
+            },
+            _ => (),
+        }
+        Ok((packs, obj))
+    }
+    fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        // TODO try to avoid cloning
+        self.visit_str(&*v)
+    }
+    fn visit_bytes<E>(self, v: &[u8]) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        vs!(self (Cow::Owned(v.to_owned())) Bytes (Type::Bytes | Type::ByteBuf))
+    }
+    fn visit_borrowed_bytes<E>(self, v: &'de [u8]) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        vs!(self (Cow::Borrowed(v)) Bytes (Type::Bytes | Type::ByteBuf))
+    }
+    fn visit_byte_buf<E>(self, v: Vec<u8>) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        // TODO try to avoid cloning
+        self.visit_bytes(&*v)
+    }
+    fn visit_none<E>(self) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        vs!(self {} None (Type::Option))
+    }
+    fn visit_some<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: serde::de::Deserializer<'de>,
+    {
+        todo!()
+    }
+    fn visit_unit<E>(self) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        vs!(self {} Unit (Type::Unit))
+    }
+    fn visit_newtype_struct<D>(
+        self,
+        deserializer: D
+    ) -> Result<Self::Value, D::Error>
+    where
+        D: serde::de::Deserializer<'de>,
+    {
+        todo!()
+    }
+    fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
+    where
+        A: serde::de::SeqAccess<'de>,
+    {
+        let old_collecting = self.collecting;
+        let pat = self.interp.pat;
+        let mut collecting = old_collecting;
+        let typeck = self.frames_mut().iter_active_mut().try_for_each(|frame| {
+            let ty = frame.get_type();
+            match ty {
+                | Some((Type::Seq, _))
+                | Some((Type::Any, _))
+                | Some((Type::IgnoredAny, _))
+                | None
+                => {},
+                Some((_, false)) => {
+                    frame.matches = false;
+                    return Ok(());
+                },
+                Some((_, true)) => {
+                    return Err(MatchError::ValidationError)
+                },
+            }
+            if frame.get_name(pat).is_some() {
+                collecting = true;
+            }
+            Ok(())
+        });
+        match typeck {
+            Err(e) => {
+                self.interp.error.insert(e);
+                return Err(A::Error::custom("type mismatch"));
+            },
+            _ => (),
+        }
+        if let Err(e) = self.step_in() { return Err(e); }
+        self.collecting = collecting;
+        let mut subframes = Vec::new();
+        let mut output_matches = Vec::new();
+        self.frames().iter_active().for_each(|frame| {
+            if let Some((key_subtree, _)) = frame.key_subtree() {
+                subframes.push(Frame {
+                    ops: &pat.protos[key_subtree],
+                    iar: None,
+                    overstep: 0,
+                    matches: true,
+                    poison: false,
+                });
+            }
+            output_matches.push(false);
+        });
+        let mut obj_inner = Vec::new();
+        let mut output_packs = Vec::new();
+        let mut iter = 0..;
+        while let packed_key = {
+            let subinterp = Interpreter {
+                pat: pat,
+                frames: &mut subframes,
+                error: self.interp.error,
+            };
+            let mut subpacker = Packer {
+                interp: subinterp,
+                collecting: self.collecting,
+                call_limit: self.call_limit,
+            };
+            if subpacker.interp.frames.is_empty() {
+                // avoid overflow
+                serde::de::DeserializeSeed::deserialize(&mut subpacker, {
+                    serde::de::value::U64Deserializer::new(0)
+                })?
+            } else {
+                serde::de::DeserializeSeed::deserialize(&mut subpacker, {
+                    serde::de::value::U64Deserializer::new(iter.next().unwrap())
+                })?
+            }
+        } {
+            self.frames_mut().iter_active_mut().filter(|frame| {
+                frame.key_subtree().is_some()
+            }).zip(&mut subframes).for_each(|(frame, subframe)| {
+                frame.matches = subframe.matches;
+                // reset subframe for next iteration
+                // NOTE wait to reset subframe.matches when merging packs!!!
+                subframe.iar = None;
+            });
+            self.frames_mut().iter_active_mut().for_each(|frame| {
+                // mark every non-subtree key as matching.
+                if frame.key_subtree().is_none() {
+                    frame.matches = true;
+                }
+            });
+            let Some(packed_value) = seq.next_element_seed(&mut *self)? else {
+                break;
+            };
+            if self.collecting {
+                obj_inner.push(packed_value.1.unwrap());
+            }
+            let mut key_packs_per_frame = packed_key.0.into_iter();
+            let mut value_packs_per_frame = packed_value.0.into_iter();
+            // whatever is active in self.frames(), if matches, has a pack
+            // whatever is in subframes, if matches, has a pack
+            // count(active self.frames() with subtree which match) is always
+            // smaller than count(subframes which match) because the former
+            // gets updated by next_value_seed
+            // count(active self.frames() with subtree) == count(subframes)
+            // tl;dr: need to figure out which packs produced by subframes line
+            // up with which packs produced by self, discarding extra subframes
+            // (where the corresponding self frame doesn't match) and accepting
+            // extra packs produced by self.
+            // NOTE: key_packs_per_frame ~ subframes
+            // value_packs_per_frame ~ self
+            // keys come first tho (key.merge_from(value))
+            let mut iter_subframes = subframes.iter_mut();
+            // related to output_packs
+            let mut pack_index = 0;
+            for (frame, out_matches) in self.frames().iter_active().zip({
+                &mut output_matches
+            }) {
+                // check if this frame has an associated subframe
+                let subframe = if frame.key_subtree().is_some() {
+                    // if there are more frames with associated subframes
+                    // than there are subframes, panic
+                    Some(iter_subframes.next().unwrap())
+                } else {
+                    None
+                };
+                let mut new_pack = None;
+                if frame.matches && subframe.is_some() {
+                    // this already implies subframe.matches
+                    let mut key_pack = key_packs_per_frame.next().unwrap();
+                    let value_pack = value_packs_per_frame.next().unwrap();
+                    key_pack.cartesian_product(value_pack);
+                    new_pack = Some(key_pack);
+                } else if frame.matches {
+                    // value matches but there's no subframe, carry on
+                    let value_pack = value_packs_per_frame.next().unwrap();
+                    new_pack = Some(value_pack);
+                } else if !frame.matches && subframe.is_some() {
+                    // frame didn't match but there was a subframe
+                    let subframe = subframe.unwrap();
+                    if subframe.matches {
+                        // subframe matched, remove key pack
+                        let _ = key_packs_per_frame.next().unwrap();
+                    } else {
+                        // neither matched, no relevant packs
+                        // do reset subframe for next_key_seed tho!
+                        subframe.matches = true;
+                    }
+                } else {
+                    // no relevant packs
+                }
+                if let Some(new_pack) = new_pack {
+                    if !*out_matches {
+                        *out_matches = true;
+                        output_packs.insert(pack_index, Pack::default());
+                    }
+                    let output_pack = &mut output_packs[pack_index];
+                    output_pack.subpacks.extend(new_pack.subpacks);
+                }
+                if *out_matches {
+                    pack_index += 1;
+                }
+            }
+        }
+        let mut poison = false;
+        for (f, m) in self.frames_mut().iter_active_mut().zip(output_matches) {
+            f.matches = m;
+            if !m {
+                if let Some((_, false)) = f.key_subtree() {
+                    poison = true;
+                }
+            }
+        }
+        let obj = SerdeObject::Seq(obj_inner);
+        let mut final_packs = self.step_out(output_packs)?;
+        let mut iter_final_packs = 0..;
+        self.frames_mut().iter_active_mut().for_each(|frame| {
+            let ty = frame.get_type();
+            match ty {
+                | Some((Type::Seq, _))
+                | Some((Type::Any, _))
+                | Some((Type::IgnoredAny, _))
+                | None
+                => {
+                    frame.poison = poison;
+                    let matched = std::mem::replace(&mut frame.matches, true);
+                    if !matched {
+                        final_packs.insert(
+                            iter_final_packs.start,
+                            Pack::default(),
+                        );
+                    }
+                },
+                _ => return,
+            }
+            let pack = &mut final_packs[iter_final_packs.next().unwrap()];
+            if let Some(name) = frame.get_name(pat) {
+                // we can assume collecting == true
+                let old_pack = std::mem::take(pack);
+                let mut map = IndexMap::new();
+                map.insert(name, obj.clone());
+                pack.subpacks.push_back((map, old_pack));
+            }
+        });
+        self.collecting = old_collecting;
+        Ok((final_packs, collecting.then(|| obj)))
+    }
+    fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+    where
+        A: serde::de::MapAccess<'de>,
+    {
+        let old_collecting = self.collecting;
+        let pat = self.interp.pat;
+        let mut collecting = old_collecting;
+        let typeck = self.frames_mut().iter_active_mut().try_for_each(|frame| {
+            let ty = frame.get_type();
+            match ty {
+                | Some((Type::Map, _))
+                | Some((Type::Any, _))
+                | Some((Type::IgnoredAny, _))
+                | None
+                => {},
+                Some((_, false)) => {
+                    frame.matches = false;
+                    return Ok(());
+                },
+                Some((_, true)) => {
+                    return Err(MatchError::ValidationError)
+                },
+            }
+            if frame.get_name(pat).is_some() {
+                collecting = true;
+            }
+            Ok(())
+        });
+        match typeck {
+            Err(e) => {
+                self.interp.error.insert(e);
+                return Err(A::Error::custom("type mismatch"));
+            },
+            _ => (),
+        }
+        if let Err(e) = self.step_in() { return Err(e); }
+        self.collecting = collecting;
+        let mut subframes = Vec::new();
+        let mut output_matches = Vec::new();
+        self.frames().iter_active().for_each(|frame| {
+            if let Some((key_subtree, _)) = frame.key_subtree() {
+                subframes.push(Frame {
+                    ops: &pat.protos[key_subtree],
+                    iar: None,
+                    overstep: 0,
+                    matches: true,
+                    poison: false,
+                });
+            }
+            output_matches.push(false);
+        });
+        let mut obj_inner = Vec::new();
+        let mut output_packs = Vec::new();
+        while let Some(packed_key) = {
+            let subinterp = Interpreter {
+                pat: pat,
+                frames: &mut subframes,
+                error: self.interp.error,
+            };
+            let mut subpacker = Packer {
+                interp: subinterp,
+                collecting: self.collecting,
+                call_limit: self.call_limit,
+            };
+            map.next_key_seed(&mut subpacker)?
+        } {
+            self.frames_mut().iter_active_mut().filter(|frame| {
+                frame.key_subtree().is_some()
+            }).zip(&mut subframes).for_each(|(frame, subframe)| {
+                frame.matches = subframe.matches;
+                // reset subframe for next iteration
+                // NOTE wait to reset subframe.matches when merging packs!!!
+                subframe.iar = None;
+            });
+            self.frames_mut().iter_active_mut().for_each(|frame| {
+                // mark every non-subtree key as matching.
+                if frame.key_subtree().is_none() {
+                    frame.matches = true;
+                }
+            });
+            let packed_value = map.next_value_seed(&mut *self)?;
+            if self.collecting {
+                obj_inner.push(
+                    (packed_key.1.unwrap(), packed_value.1.unwrap()),
+                );
+            }
+            let mut key_packs_per_frame = packed_key.0.into_iter();
+            let mut value_packs_per_frame = packed_value.0.into_iter();
+            // whatever is active in self.frames(), if matches, has a pack
+            // whatever is in subframes, if matches, has a pack
+            // count(active self.frames() with subtree which match) is always
+            // smaller than count(subframes which match) because the former
+            // gets updated by next_value_seed
+            // count(active self.frames() with subtree) == count(subframes)
+            // tl;dr: need to figure out which packs produced by subframes line
+            // up with which packs produced by self, discarding extra subframes
+            // (where the corresponding self frame doesn't match) and accepting
+            // extra packs produced by self.
+            // NOTE: key_packs_per_frame ~ subframes
+            // value_packs_per_frame ~ self
+            // keys come first tho (key.merge_from(value))
+            let mut iter_subframes = subframes.iter_mut();
+            // related to output_packs
+            let mut pack_index = 0;
+            for (frame, out_matches) in self.frames().iter_active().zip({
+                &mut output_matches
+            }) {
+                // check if this frame has an associated subframe
+                let subframe = if frame.key_subtree().is_some() {
+                    // if there are more frames with associated subframes
+                    // than there are subframes, panic
+                    Some(iter_subframes.next().unwrap())
+                } else {
+                    None
+                };
+                let mut new_pack = None;
+                if frame.matches && subframe.is_some() {
+                    // this already implies subframe.matches
+                    let mut key_pack = key_packs_per_frame.next().unwrap();
+                    let value_pack = value_packs_per_frame.next().unwrap();
+                    key_pack.cartesian_product(value_pack);
+                    new_pack = Some(key_pack);
+                } else if frame.matches {
+                    // value matches but there's no subframe, carry on
+                    let value_pack = value_packs_per_frame.next().unwrap();
+                    new_pack = Some(value_pack);
+                } else if !frame.matches && subframe.is_some() {
+                    // frame didn't match but there was a subframe
+                    let subframe = subframe.unwrap();
+                    if subframe.matches {
+                        // subframe matched, remove key pack
+                        let _ = key_packs_per_frame.next().unwrap();
+                    } else {
+                        // neither matched, no relevant packs
+                        // do reset subframe for next_key_seed tho!
+                        subframe.matches = true;
+                    }
+                } else {
+                    // no relevant packs
+                }
+                if let Some(new_pack) = new_pack {
+                    if !*out_matches {
+                        *out_matches = true;
+                        output_packs.insert(pack_index, Pack::default());
+                    }
+                    let output_pack = &mut output_packs[pack_index];
+                    output_pack.subpacks.extend(new_pack.subpacks);
+                }
+                if *out_matches {
+                    pack_index += 1;
+                }
+            }
+        }
+        let mut poison = false;
+        for (f, m) in self.frames_mut().iter_active_mut().zip(output_matches) {
+            f.matches = m;
+            if !m {
+                if let Some((_, false)) = f.key_subtree() {
+                    poison = true;
+                }
+            }
+        }
+        let obj = SerdeObject::Map(obj_inner);
+        let mut final_packs = self.step_out(output_packs)?;
+        let mut iter_final_packs = 0..;
+        self.frames_mut().iter_active_mut().for_each(|frame| {
+            let ty = frame.get_type();
+            match ty {
+                | Some((Type::Map, _))
+                | Some((Type::Any, _))
+                | Some((Type::IgnoredAny, _))
+                | None
+                => {
+                    frame.poison = poison;
+                    let matched = std::mem::replace(&mut frame.matches, true);
+                    if !matched {
+                        final_packs.insert(
+                            iter_final_packs.start,
+                            Pack::default(),
+                        );
+                    }
+                },
+                _ => return,
+            }
+            let pack = &mut final_packs[iter_final_packs.next().unwrap()];
+            if let Some(name) = frame.get_name(pat) {
+                // we can assume collecting == true
+                let old_pack = std::mem::take(pack);
+                let mut map = IndexMap::new();
+                map.insert(name, obj.clone());
+                pack.subpacks.push_back((map, old_pack));
+            }
+        });
+        self.collecting = old_collecting;
+        Ok((final_packs, collecting.then(|| obj)))
+    }
+    fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
+    where
+        A: serde::de::EnumAccess<'de>,
+    {
+        let mut obj = None;
+        if self.collecting {
+            obj = Some(SerdeObject::Enum {
+                variant: todo!(),
+                data: todo!(),
+            });
+        }
+        todo!()
+    }
+}
+
+/// Deserializes a SerdeObject
+pub(crate) struct SerdeObjectDeserializer<'de, E> {
+    pub(crate) obj: SerdeObject<'de>,
+    pub(crate) _e: PhantomData<fn() -> E>,
+}
+
+/// Deserializes a SerdeObject::Seq
+struct SerdeObjectSeq<'de, I: Iterator<Item=SerdeObject<'de>>, E> {
+    iter: I,
+    _e: PhantomData<fn() -> E>,
+}
+
+impl<'de, E> serde::de::VariantAccess<'de> for SerdeObjectDeserializer<'de, E>
+where
+    E: serde::de::Error,
+{
+    type Error = E;
+
+    fn unit_variant(self) -> Result<(), E> {
+        todo!()
+    }
+    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value, E>
+    where
+        T: serde::de::DeserializeSeed<'de>,
+    {
+        todo!()
+    }
+    fn tuple_variant<V>(self, len: usize, visitor: V) -> Result<V::Value, E>
+    where
+        V: serde::de::Visitor<'de>,
+    {
+        todo!()
+    }
+    fn struct_variant<V>(
+        self,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, E>
+    where
+        V: serde::de::Visitor<'de>,
+    {
+        todo!()
+    }
+}
+
+impl<'de, E> serde::de::EnumAccess<'de> for SerdeObjectDeserializer<'de, E>
+where
+    E: serde::de::Error,
+{
+    type Error = E;
+    type Variant = Self;
+
+    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self), E>
+    where
+        V: serde::de::DeserializeSeed<'de>,
+    {
+        match self.obj {
+            SerdeObject::Enum { variant, data } => {
+                seed.deserialize(variant.into_deserializer()).map(|it| {
+                    let data = Self {
+                        obj: *data,
+                        _e: PhantomData,
+                    };
+                    (it, data)
+                })
+            },
+            _ => unreachable!(),
+        }
+    }
+}
+
+impl<'de, E> serde::de::Deserializer<'de> for SerdeObjectDeserializer<'de, E>
+where
+    E: serde::de::Error,
+{
+    type Error = E;
+    fn deserialize_any<V>(self, v: V) -> Result<V::Value, Self::Error>
+    where
+        V: serde::de::Visitor<'de>,
+    {
+        match self.obj {
+            SerdeObject::Bool(x) => v.visit_bool(x),
+            SerdeObject::I8(x) => v.visit_i8(x),
+            SerdeObject::I16(x) => v.visit_i16(x),
+            SerdeObject::I32(x) => v.visit_i32(x),
+            SerdeObject::I64(x) => v.visit_i64(x),
+            SerdeObject::I128(x) => v.visit_i128(x),
+            SerdeObject::U8(x) => v.visit_u8(x),
+            SerdeObject::U16(x) => v.visit_u16(x),
+            SerdeObject::U32(x) => v.visit_u32(x),
+            SerdeObject::U64(x) => v.visit_u64(x),
+            SerdeObject::U128(x) => v.visit_u128(x),
+            SerdeObject::F32(x) => v.visit_f32(x),
+            SerdeObject::F64(x) => v.visit_f64(x),
+            SerdeObject::Char(x) => v.visit_char(x),
+            SerdeObject::Str(Cow::Owned(x)) => v.visit_string(x),
+            SerdeObject::Str(Cow::Borrowed(x)) => v.visit_borrowed_str(x),
+            SerdeObject::Bytes(Cow::Owned(x)) => v.visit_byte_buf(x),
+            SerdeObject::Bytes(Cow::Borrowed(x)) => v.visit_borrowed_bytes(x),
+            SerdeObject::Some(x) => v.visit_some(x.into_deserializer()),
+            SerdeObject::None => v.visit_none(),
+            SerdeObject::Unit => v.visit_unit(),
+            SerdeObject::Seq(x) => {
+                let mut x = serde::de::value::SeqDeserializer::new(x.into_iter());
+                let r = v.visit_seq(&mut x);
+                x.end().and(r)
+            },
+            SerdeObject::Map(x) => {
+                let mut x = serde::de::value::MapDeserializer::new(x.into_iter());
+                let r = v.visit_map(&mut x);
+                x.end().and(r)
+            },
+            SerdeObject::NewtypeStruct(x) => {
+                v.visit_newtype_struct(x.into_deserializer())
+            },
+            SerdeObject::Enum { .. } => v.visit_enum(self),
+        }
+    }
+    fn deserialize_ignored_any<V>(self, v: V) -> Result<V::Value, Self::Error>
+    where
+        V: serde::de::Visitor<'de>,
+    {
+        drop(self);
+        v.visit_unit()
+    }
+    serde::forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct enum identifier
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Packer;
+    use super::super::PatternConstants;
+
+    use crate::vm::MAX_CALLS;
+    use crate::vm::Interpreter;
+    use crate::vm::Type;
+    use crate::vm::Value;
+    use crate::vm::PatternElement;
+    use crate::vm::SerdeObject;
+    use crate::vm::Frame;
+
+    use postcard::Deserializer as PostcardDeserializer;
+    use serde::de::DeserializeSeed as _;
+    use serde_json::Deserializer as JsonDeserializer;
+
+    use crate::errors::MatchError;
+
+    #[test]
+    #[should_panic]
+    fn test_broken() {
+        // broken pattern, should never be emitted by parser. make sure it's
+        // not accepted.
+        let consts = PatternConstants::<()>::default();
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(&consts, &mut err, &mut frames);
+        let _ = Packer::new(interp, MAX_CALLS);
+    }
+
+    #[test]
+    fn test_empty_create() {
+        // test creating the parser with an empty pattern.
+        let mut consts = PatternConstants::<()>::default();
+        consts.protos.push(Vec::new());
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(&consts, &mut err, &mut frames);
+        let _ = Packer::new(interp, MAX_CALLS);
+    }
+
+    #[test]
+    fn test_empty_match() {
+        // test matching something with an empty pattern.
+        let mut consts = PatternConstants::<()>::default();
+        consts.protos.push(Vec::new());
+        let mut der = JsonDeserializer::from_str("{}");
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(&consts, &mut err, &mut frames);
+        let pack = Packer::new(interp, MAX_CALLS).deserialize(&mut der).unwrap();
+    }
+
+    #[test]
+    fn test_simple_match() {
+        // test matching a simple value
+        let mut consts = PatternConstants::<()>::default();
+        consts.strings.insert("hello".into());
+        consts.protos.push(vec![
+            PatternElement::Value {
+                name: Some(0),
+                value: Some(Value::Type {
+                    ty: Type::U64,
+                    skippable: false,
+                }),
+            },
+        ]);
+        let mut der = JsonDeserializer::from_str("3");
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(&consts, &mut err, &mut frames);
+        let packed = Packer::new(interp, MAX_CALLS).deserialize(&mut der);
+        let (packs, obj) = packed.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(
+            packs[0].get_object_at(0, "hello").unwrap(),
+            &SerdeObject::U64(3),
+        );
+    }
+
+    #[test]
+    fn test_simple_error() {
+        // test a value that doesn't match (serde_json error)
+        let mut consts = PatternConstants::<()>::default();
+        consts.strings.insert("hello".into());
+        consts.protos.push(vec![
+            PatternElement::Value {
+                name: Some(0),
+                value: Some(Value::Type {
+                    ty: Type::U64,
+                    skippable: false,
+                }),
+            },
+        ]);
+        let mut der = JsonDeserializer::from_str("\"hello\"");
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(&consts, &mut err, &mut frames);
+        let packed = Packer::new(interp, MAX_CALLS).deserialize(&mut der);
+        // error produced by serde_json
+        assert!(packed.is_err());
+    }
+
+    #[test]
+    fn test_basic_multiframe() {
+        // test multiple frames (matching and non-matching)
+        let mut consts = PatternConstants::<()>::default();
+        consts.strings.insert("a".into());
+        consts.strings.insert("b".into());
+        consts.protos.push(vec![
+            PatternElement::Value {
+                name: Some(0),
+                value: Some(Value::Type {
+                    ty: Type::U64,
+                    skippable: true,
+                }),
+            },
+        ]);
+        consts.protos.push(vec![
+            PatternElement::Value {
+                name: Some(1),
+                value: Some(Value::Type {
+                    ty: Type::Bool,
+                    skippable: true,
+                }),
+            },
+        ]);
+        let mut der = JsonDeserializer::from_str(r#"10"#);
+        let mut err = Default::default();
+        let mut frames: Vec<_> = Default::default();
+        frames.push(Frame {
+            ops: &consts.protos[0],
+            iar: None,
+            matches: true,
+            overstep: 0,
+            poison: false,
+        });
+        frames.push(Frame {
+            ops: &consts.protos[1],
+            iar: None,
+            matches: true,
+            overstep: 0,
+            poison: false,
+        });
+        let interp = Interpreter {
+            pat: &consts,
+            error: &mut err,
+            frames: &mut frames,
+        };
+        let packed = Packer::new(interp, MAX_CALLS).deserialize(&mut der);
+        let (packs, obj) = packed.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(
+            packs[0].get_object_at(0, "a").unwrap(),
+            &SerdeObject::U64(10),
+        );
+        assert_eq!(packs.len(), 1);
+        assert!(frames[0].matches);
+        assert!(!frames[1].matches);
+    }
+
+    #[test]
+    fn test_map() {
+        // test visit_map
+        let mut consts = PatternConstants::<()>::default();
+        consts.strings.insert("key".into());
+        consts.strings.insert("value".into());
+        consts.protos.push(vec![
+            PatternElement::Value {
+                name: Some(0),
+                value: None,
+            },
+        ]);
+        consts.protos.push(vec![
+            PatternElement::Value {
+                name: None,
+                value: Some(Value::Type {
+                    ty: Type::Map,
+                    skippable: false,
+                }),
+            },
+            PatternElement::Tag {
+                key_subtree: 0,
+                optional: true,
+            },
+            PatternElement::Value {
+                name: Some(1),
+                value: Some(Value::Type {
+                    ty: Type::U64,
+                    skippable: false,
+                }),
+            },
+        ]);
+        let mut der = JsonDeserializer::from_str(r#"{"hello": 0, "world": 1}"#);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(&consts, &mut err, &mut frames);
+        let packed = Packer::new(interp, MAX_CALLS).deserialize(&mut der);
+        let (packs, obj) = packed.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(
+            packs[0].get_object_at(0, "key").unwrap(),
+            &SerdeObject::Str("hello".into()),
+        );
+        assert_eq!(
+            packs[0]
+                .get_object_at(0, "value").unwrap(),
+            &SerdeObject::U64(0),
+        );
+        assert_eq!(
+            packs[0].get_object_at(1, "key").unwrap(),
+            &SerdeObject::Str("world".into()),
+        );
+        assert_eq!(
+            packs[0]
+                .get_object_at(1, "value").unwrap(),
+            &SerdeObject::U64(1),
+        );
+    }
+
+    #[test]
+    fn test_parser_empty() {
+        // use a parsed empty pattern to test Packer
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            "",
+            None,
+            None,
+        ).unwrap();
+        let mut der = JsonDeserializer::from_str(r#"{"hello": 0, "world": 1}"#);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let (mut packs, obj) = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der).unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = packs.pop().unwrap();
+        assert!(pack.subpacks.is_empty());
+    }
+
+    #[test]
+    fn test_parser_basic() {
+        // use a basic parsed pattern to test Packer
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            ":map->[name:str]value:str",
+            None,
+            None,
+        ).unwrap();
+        let data = &[
+            0x02, // map length (2)
+            0x04, // string length (4)
+            0x6E, 0x61, 0x6D, 0x65, // b'name'
+            0x01, // string length (1)
+            0x61, // b'a'
+            0x05, // string length (5)
+            0x76, 0x61, 0x6C, 0x75, 0x65, // b'value'
+            0x01, // string length (1)
+            0x62, // b'b'
+        ];
+        let mut der = PostcardDeserializer::from_bytes(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = packs.pop().unwrap();
+        assert_eq!(pack.subpacks.len(), 2);
+    }
+
+    #[test]
+    fn test_parser_basic_subtree() {
+        // use a basic parsed pattern with a subtree to test Packer
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            ":map(->[name:str]value:str)",
+            None,
+            None,
+        ).unwrap();
+        let data = &[
+            0x02, // map length (2)
+            0x04, // string length (4)
+            0x6E, 0x61, 0x6D, 0x65, // b'name'
+            0x01, // string length (1)
+            0x61, // b'a'
+            0x05, // string length (5)
+            0x76, 0x61, 0x6C, 0x75, 0x65, // b'value'
+            0x01, // string length (1)
+            0x62, // b'b'
+        ];
+        let mut der = PostcardDeserializer::from_bytes(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = packs.pop().unwrap();
+        assert_eq!(pack.subpacks.len(), 2);
+    }
+
+    #[test]
+    fn test_empty_subtrees() {
+        // tests empty subtrees
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            ":map()(())",
+            None,
+            None,
+        ).unwrap();
+        let data = r#"{"hello": "world"}"#;
+        let mut der = JsonDeserializer::from_str(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = packs.pop().unwrap();
+        assert_eq!(pack.subpacks.len(), 0);
+    }
+
+    #[test]
+    fn test_parser_subtrees() {
+        // use a parsed pattern with subtrees to test Packer
+        // also test a non-self-describing format (postcard)
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            ":map(->['name'?]name:str)?(->['value'?]value:u32)?(->[:str]:?ignored_any)",
+            None,
+            None,
+        ).unwrap();
+        let data = &[
+            0x02, // map length (2)
+            0x04, // string length (4)
+            0x6E, 0x61, 0x6D, 0x65, // b'name'
+            0x01, // string length (1)
+            0x61, // b'a'
+            0x05, // string length (5)
+            0x76, 0x61, 0x6C, 0x75, 0x65, // b'value'
+            0x01, // 1
+        ];
+        let mut der = PostcardDeserializer::from_bytes(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = packs.pop().unwrap();
+        assert_eq!(pack.subpacks.len(), 1);
+        assert_eq!(
+            pack.get_object_at(0, "name").unwrap(),
+            &SerdeObject::Str(From::from("a")),
+        );
+        assert_eq!(
+            pack.get_object_at(0, "value").unwrap(),
+            &SerdeObject::U32(1),
+        );
+    }
+
+    #[test]
+    fn test_parser_subtrees_validation() {
+        // checks that the Packer can validate multiple keys.
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            ":map(->['name'?]name:str)(->['value'?]value:u32)(->[:str]:?ignored_any)",
+            None,
+            None,
+        ).unwrap();
+        let data = &[
+            0x02, // map length (2)
+            0x04, // string length (4)
+            0x6E, 0x61, 0x6D, 0x65, // b'name'
+            0x01, // string length (1)
+            0x61, // b'a'
+            0x05, // string length (5)
+            0x76, 0x61, 0x6C, 0x75, 0x65, // b'value'
+            0x01, // 1
+        ];
+        let mut der = PostcardDeserializer::from_bytes(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = packs.pop().unwrap();
+        assert_eq!(pack.subpacks.len(), 1);
+        assert_eq!(
+            pack.get_object_at(0, "name").unwrap(),
+            &SerdeObject::Str(From::from("a")),
+        );
+        assert_eq!(
+            pack.get_object_at(0, "value").unwrap(),
+            &SerdeObject::U32(1),
+        );
+    }
+
+    #[test]
+    fn test_one_or_more_subtrees_validation() {
+        // checks that the Packer supports OR-like validation semantics
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            ":map((->['name'?]?name)?(->['value'?]?value)?)(->[:str]:u32)",
+            None,
+            None,
+        ).unwrap();
+        let data = &[
+            0x01, // map length (1)
+            0x04, // string length (4)
+            0x6E, 0x61, 0x6D, 0x65, // b'name'
+            0x01, // 1
+        ];
+        let mut der = PostcardDeserializer::from_bytes(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = packs.pop().unwrap();
+        assert_eq!(pack.subpacks.len(), 1);
+        assert_eq!(
+            pack.get_object_at(0, "name").unwrap(),
+            &SerdeObject::U32(1),
+        );
+    }
+
+    #[test]
+    fn test_one_or_more_subtrees_validation_failure() {
+        // checks that the Packer supports OR-like validation semantics
+        // (failure)
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            ":map((->['name'?]?name)?(->['value'?]?value)?)(->[:str]:u32)",
+            None,
+            None,
+        ).unwrap();
+        let data = &[
+            0x01, // map length (1)
+            0x04, // string length (4)
+            0x6E, 0x65, 0x6D, 0x65, // b'neme'
+            0x01, // 1
+        ];
+        let mut der = PostcardDeserializer::from_bytes(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        assert!(matches!(err, Some(MatchError::ValidationError)));
+        assert!(result.is_err());
+    }
+
+    // FIXME this should test that the map doesn't contain other keys aside
+    // from the ones requested by the pattern, but this doesn't match existing
+    // datafu semantics at all. we need new syntax for it.
+    //#[test]
+    //fn test_parser_subtrees_no_additional_keys() {
+    //    // use a parsed pattern with subtrees to test Packer
+    //    // also test a non-self-describing format (postcard)
+    //    // also require at least one subtree to match on every iteration.
+    //    // also this checks for validation error
+    //    let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+    //        ":map((->['name'?]name)?(->['value'?]value)?)(->[:str]:u32)",
+    //        None,
+    //        None,
+    //    ).unwrap();
+    //    let data = &[
+    //        0x03, // map length (3)
+    //        0x04, // string length (4)
+    //        0x6E, 0x61, 0x6D, 0x65, // b'name'
+    //        0x01, // 1
+    //        0x05, // string length (5)
+    //        0x76, 0x61, 0x6C, 0x75, 0x65, // b'value'
+    //        0x01, // 1
+    //        0x05, // string length (5)
+    //        0x76, 0x65, 0x6C, 0x75, 0x65, // b'velue'
+    //        0x01, // 1
+    //    ];
+    //    let mut der = PostcardDeserializer::from_bytes(data);
+    //    let mut err = Default::default();
+    //    let mut frames = Default::default();
+    //    let interp = Interpreter::new(
+    //        &consts,
+    //        &mut err,
+    //        &mut frames,
+    //        //&mut output,
+    //    );
+    //    let result = Packer::new(
+    //        interp,
+    //        MAX_CALLS,
+    //    ).deserialize(&mut der);
+    //    assert!(matches!(err, Some(MatchError::ValidationError)));
+    //    assert!(result.is_err());
+    //}
+
+    #[test]
+    fn test_key_optionally_missing() {
+        // test a pattern with a missing key
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            "
+            :map
+            ->['a'?]:map
+              ->[b:?str]:?map
+                (->['x'?]x:?bool)?
+                (->['y'?]?y:?bool)?
+            ",
+            None,
+            None
+        ).unwrap();
+        let data = r#"{"a": {"1": {"y": true}, "2": {"x": true, "y": true}}}"#;
+        let mut der = JsonDeserializer::from_str(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = &packs[0];
+        assert_eq!(pack.subpacks.len(), 1);
+        assert_eq!(
+            pack.get_object_at(0, "b").unwrap(),
+            &SerdeObject::Str(From::from("2")),
+        );
+        assert_eq!(
+            pack.get_object_at(0, "x").unwrap(),
+            &SerdeObject::Bool(true),
+        );
+        assert_eq!(
+            pack.get_object_at(0, "y").unwrap(),
+            &SerdeObject::Bool(true),
+        );
+    }
+
+    #[test]
+    fn test_map_without_values() {
+        // test that the map without values still collects the key
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            "
+            :map
+            ->[a:?str]?:?map
+              ->[b:?str]?:?map
+            ",
+            None,
+            None
+        ).unwrap();
+        let data = r#"{"a": {}}"#;
+        let mut der = JsonDeserializer::from_str(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = &packs[0];
+        assert_eq!(pack.subpacks.len(), 1);
+        assert_eq!(
+            pack.get_object_at(0, "a").unwrap(),
+            &SerdeObject::Str(From::from("a")),
+        );
+        assert_eq!(pack.get_subpack_at(0, "a").unwrap().subpacks.len(), 0);
+    }
+
+    #[test]
+    fn test_guaranteed_at_least_once() {
+        // test that at least one match is required before collecting the key
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            "
+            :map
+            ->[a:?str]:?map
+              ->[b:?str]:?map
+            ",
+            None,
+            None
+        ).unwrap();
+        let data = r#"{"a": {}}"#;
+        let mut der = JsonDeserializer::from_str(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 0);
+    }
+
+    #[test]
+    fn test_basic_seq() {
+        // test that sequences work
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            "
+            :seq
+            ->[i:u64]v:u64
+            ",
+            None,
+            None
+        ).unwrap();
+        let data = r#"[10, 11, 12]"#;
+        let mut der = JsonDeserializer::from_str(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = packs.pop().unwrap();
+        assert_eq!(pack.subpacks.len(), 3);
+        assert_eq!(
+            pack.get_object_at(0, "i").unwrap(),
+            &SerdeObject::U64(0),
+        );
+        assert_eq!(
+            pack.get_object_at(0, "v").unwrap(),
+            &SerdeObject::U64(10),
+        );
+        assert_eq!(
+            pack.get_object_at(1, "i").unwrap(),
+            &SerdeObject::U64(1),
+        );
+        assert_eq!(
+            pack.get_object_at(1, "v").unwrap(),
+            &SerdeObject::U64(11),
+        );
+        assert_eq!(
+            pack.get_object_at(2, "i").unwrap(),
+            &SerdeObject::U64(2),
+        );
+        assert_eq!(
+            pack.get_object_at(2, "v").unwrap(),
+            &SerdeObject::U64(12),
+        );
+    }
+
+    #[test]
+    fn test_list_key() {
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            "
+            :map
+            ->[:seq->k:u64]:seq
+              ->v:str
+            ",
+            None,
+            None
+        ).unwrap();
+        let data = &[
+            0x01, // map length (1)
+            0x03, // list length (3)
+            0x01, 0x02, 0x03, // [1, 2, 3]
+            0x02, // list length (2)
+            0x05, // string length (5)
+            b't', b'r', b'a', b'n', b's',
+            0x06, // string length (6)
+            b'r', b'i', b'g', b'h', b't', b's'
+        ];
+        let mut der = PostcardDeserializer::from_bytes(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = packs.pop().unwrap();
+        assert_eq!(pack.subpacks.len(), 3);
+        let subpack = pack.get_subpack_at(0, "k").unwrap();
+        assert_eq!(subpack.subpacks.len(), 2);
+        assert_eq!(
+            pack.get_object_at(0, "k").unwrap(),
+            &SerdeObject::U64(1),
+        );
+        assert_eq!(
+            subpack.get_object_at(0, "v").unwrap(),
+            &SerdeObject::Str(From::from("trans")),
+        );
+        assert_eq!(
+            subpack.get_object_at(1, "v").unwrap(),
+            &SerdeObject::Str(From::from("rights")),
+        );
+        let subpack = pack.get_subpack_at(1, "k").unwrap();
+        assert_eq!(subpack.subpacks.len(), 2);
+        assert_eq!(
+            pack.get_object_at(1, "k").unwrap(),
+            &SerdeObject::U64(2),
+        );
+        assert_eq!(
+            subpack.get_object_at(0, "v").unwrap(),
+            &SerdeObject::Str(From::from("trans")),
+        );
+        assert_eq!(
+            subpack.get_object_at(1, "v").unwrap(),
+            &SerdeObject::Str(From::from("rights")),
+        );
+        let subpack = pack.get_subpack_at(2, "k").unwrap();
+        assert_eq!(subpack.subpacks.len(), 2);
+        assert_eq!(
+            pack.get_object_at(2, "k").unwrap(),
+            &SerdeObject::U64(3),
+        );
+        assert_eq!(
+            subpack.get_object_at(0, "v").unwrap(),
+            &SerdeObject::Str(From::from("trans")),
+        );
+        assert_eq!(
+            subpack.get_object_at(1, "v").unwrap(),
+            &SerdeObject::Str(From::from("rights")),
+        );
+    }
+
+    #[test]
+    fn test_realish_use_case() {
+        // use a parsed pattern that might actually be used in the real world.
+        let consts = crate::parser::parse::<&'static str, &'static str, ()>(
+            "
+            :map
+            ->['projects'?]:map
+              ->[commit:?str]:?map
+                ->[url:?str]:?map
+                  ->[branch:?str]:?map
+                    (->['active'?]active:?bool)?
+                    (->['federate'?]?federate:?bool)?
+            ",
+            None,
+            None
+        ).unwrap();
+        let data = r#"
+        {"base_url": "https://ganarchy.autistic.space", "repo_list_srcs": {"https://ganarchy.autistic.space/index.toml": {"active": false}}, "projects": {"385e734a52e13949a7a5c71827f6de920dbfea43": {"https://github.com/ganarchy/GAnarchy": {"HEAD": {"active": true}}, "https://soniex2.autistic.space/git-repos/ganarchy.git": {"HEAD": {"active": true, "pinned": true}}}, "a8fb5087f79eafe312db270082c052c427b208c2": {"https://soniex2.autistic.space/git-repos/mmorfc.git": {"HEAD": {"active": true, "pinned": true}}}, "2d0b363fe3179087de59d9ef4a2d14af21d89071": {"https://soniex2.autistic.space/git-repos/chewstuff.git": {"HEAD": {"active": true, "pinned": true}}}}}
+        "#;
+        let mut der = JsonDeserializer::from_str(data);
+        let mut err = Default::default();
+        let mut frames = Default::default();
+        let interp = Interpreter::new(
+            &consts,
+            &mut err,
+            &mut frames,
+            //&mut output,
+        );
+        let result = Packer::new(
+            interp,
+            MAX_CALLS,
+        ).deserialize(&mut der);
+        let (mut packs, obj) = result.unwrap();
+        assert!(obj.is_none());
+        assert_eq!(packs.len(), 1);
+        let pack = &packs[0];
+        assert_eq!(pack.subpacks.len(), 3);
+
+        let commit = pack.get_subpack_at(0, "commit").unwrap();
+        assert_eq!(
+            pack.get_object_at(0, "commit").unwrap(),
+            &SerdeObject::Str(From::from("385e734a52e13949a7a5c71827f6de920dbfea43")),
+        );
+        assert_eq!(commit.subpacks.len(), 2);
+
+        assert_eq!(
+            commit.get_object_at(0, "url").unwrap(),
+            &SerdeObject::Str(From::from("https://github.com/ganarchy/GAnarchy")),
+        );
+        assert_eq!(
+            commit.get_object_at(0, "branch").unwrap(),
+            &SerdeObject::Str(From::from("HEAD")),
+        );
+        assert_eq!(
+            commit.get_object_at(0, "active").unwrap(),
+            &SerdeObject::Bool(true),
+        );
+
+        assert_eq!(
+            commit.get_object_at(1, "url").unwrap(),
+            &SerdeObject::Str(From::from("https://soniex2.autistic.space/git-repos/ganarchy.git")),
+        );
+        assert_eq!(
+            commit.get_object_at(1, "branch").unwrap(),
+            &SerdeObject::Str(From::from("HEAD")),
+        );
+        assert_eq!(
+            commit.get_object_at(1, "active").unwrap(),
+            &SerdeObject::Bool(true),
+        );
+
+        assert_eq!(
+            pack.get_object_at(1, "commit").unwrap(),
+            &SerdeObject::Str(From::from("a8fb5087f79eafe312db270082c052c427b208c2")),
+        );
+        assert_eq!(
+            pack.get_object_at(1, "url").unwrap(),
+            &SerdeObject::Str(From::from("https://soniex2.autistic.space/git-repos/mmorfc.git")),
+        );
+        assert_eq!(
+            pack.get_object_at(1, "branch").unwrap(),
+            &SerdeObject::Str(From::from("HEAD")),
+        );
+        assert_eq!(
+            pack.get_object_at(1, "active").unwrap(),
+            &SerdeObject::Bool(true),
+        );
+
+        assert_eq!(
+            pack.get_object_at(2, "commit").unwrap(),
+            &SerdeObject::Str(From::from("2d0b363fe3179087de59d9ef4a2d14af21d89071")),
+        );
+        assert_eq!(
+            pack.get_object_at(2, "url").unwrap(),
+            &SerdeObject::Str(From::from("https://soniex2.autistic.space/git-repos/chewstuff.git")),
+        );
+        assert_eq!(
+            pack.get_object_at(2, "branch").unwrap(),
+            &SerdeObject::Str(From::from("HEAD")),
+        );
+        assert_eq!(
+            pack.get_object_at(2, "active").unwrap(),
+            &SerdeObject::Bool(true),
+        );
+    }
+}
+
diff --git a/src/vm/de/unpacker.rs b/src/vm/de/unpacker.rs
new file mode 100644
index 0000000..8b16aa3
--- /dev/null
+++ b/src/vm/de/unpacker.rs
@@ -0,0 +1,518 @@
+// Copyright (C) 2022 Soni L.
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+//! Unpacker-related parts of the VM.
+
+use std::collections::HashMap;
+use std::collections::hash_map::IntoIter as HMIntoIter;
+
+use serde::de::IntoDeserializer;
+use serde::de::value::StrDeserializer;
+
+use crate::errors::QueryError;
+use crate::vm::Pack;
+
+/// A `Deserializer` for Datafu output.
+///
+/// This converts from Datafu's internal representation (a "pack") into the
+/// desired output type.
+pub struct Unpacker<'pat, 'de> {
+    packs: Vec<Pack<'pat, 'de>>,
+    call_limit: usize,
+}
+
+/// Wrapper for an `&mut Unpacker<'pat, 'de>` with additional field
+/// unpacking logic.
+struct UnpackerFields<'a, 'pat, 'de> {
+    unpacker: &'a mut Unpacker<'pat, 'de>,
+    fields: HMIntoIter<&'static str, Option<crate::vm::SerdeObject<'de>>>,
+    value: Option<crate::vm::SerdeObject<'de>>,
+}
+
+impl<'pat, 'de> Unpacker<'pat, 'de> {
+    /// Creates an Unpacker for unpacking a given Pack.
+    pub fn new(pack: Pack<'pat, 'de>, call_limit: usize) -> Self {
+        // invariant: no empty packs
+        let packs = if pack.subpacks.is_empty() {
+            vec![]
+        } else {
+            vec![pack]
+        };
+        Self {
+            packs, call_limit,
+        }
+    }
+
+    /// Takes the next subpack from the last pack in the pack stack.
+    fn take_next_pack(&mut self) -> Option<Pack<'pat, 'de>> {
+        self.packs.last_mut().and_then(|x| {
+            x.subpacks.front_mut()
+        }).map(|&mut (_, ref mut pack)| {
+            std::mem::take(pack)
+        }).filter(|pack| !pack.subpacks.is_empty())
+    }
+}
+
+impl<'pat, 'de> serde::de::SeqAccess<'de> for Unpacker<'pat, 'de> {
+    type Error = QueryError;
+
+    fn next_element_seed<T: serde::de::DeserializeSeed<'de>>(
+        &mut self,
+        seed: T,
+    ) -> Result<Option<T::Value>, Self::Error> {
+        if self.packs.is_empty() {
+            return Ok(None)
+        }
+        seed.deserialize(self).map(Some)
+    }
+}
+
+impl Drop for UnpackerFields<'_, '_, '_> {
+    fn drop(&mut self) {
+        let unpacker = &mut *self.unpacker;
+        while let Some(mut pack) = unpacker.packs.pop() {
+            pack.subpacks.pop_front();
+            if !pack.subpacks.is_empty() {
+                unpacker.packs.push(pack);
+                break;
+            }
+        }
+    }
+}
+
+impl<'pat, 'de> serde::de::MapAccess<'de> for UnpackerFields<'_, 'pat, 'de> {
+    type Error = QueryError;
+    fn next_key_seed<T: serde::de::DeserializeSeed<'de>>(
+        &mut self,
+        seed: T,
+    ) -> Result<Option<T::Value>, Self::Error> {
+        while let Some((key, value)) = self.fields.next() {
+            if value.is_some() {
+                self.value = value;
+                return seed.deserialize(StrDeserializer::new(key)).map(Some)
+            }
+        }
+        Ok(None)
+    }
+
+    fn next_value_seed<T: serde::de::DeserializeSeed<'de>>(
+        &mut self,
+        seed: T,
+    ) -> Result<T::Value, Self::Error> {
+        if let Some(value) = self.value.take() {
+            seed.deserialize(value.into_deserializer())
+        } else {
+            panic!("broken visitor")
+        }
+    }
+}
+
+impl<'pat, 'de> serde::Deserializer<'de> for &mut Unpacker<'pat, 'de> {
+    type Error = QueryError;
+    fn deserialize_any<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_bool<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_i8<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_i16<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_i32<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_i64<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_u8<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_u16<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_u32<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_u64<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_f32<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_f64<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_char<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_str<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_string<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_bytes<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_byte_buf<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_option<V: serde::de::Visitor<'de>>(
+        self,
+        visitor: V,
+    ) -> Result<V::Value, Self::Error> {
+        todo!()
+    }
+    fn deserialize_unit<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_unit_struct<V>(self, _: &'static str, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_newtype_struct<V>(self, _: &'static str, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!(); }
+    fn deserialize_tuple<V>(self, _: usize, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_tuple_struct<V>(self, _: &'static str, _: usize, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_map<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_struct<V>(
+        self,
+        name: &'static str,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: serde::de::Visitor<'de>,
+    {
+        let _ = name;
+        let mut field_map = fields.iter().copied().map(|n| {
+            (n, None::<crate::vm::SerdeObject<'de>>)
+        }).collect::<HashMap<&'static str, Option<_>>>();
+        // unroll packs
+        while let Some(pack) = self.take_next_pack() {
+            self.packs.push(pack);
+        }
+        // roll them back up
+        'roll: while let Some(pack) = self.packs.pop() {
+            let (ref entries, _) = pack.subpacks[0];
+            for key in entries.keys().copied() {
+                if field_map.contains_key(key) {
+                    self.packs.push(pack);
+                    break 'roll;
+                }
+            }
+            match self.packs.last_mut().map(|x| &mut x.subpacks[0]) {
+                Some((_, subpack)) => {
+                    *subpack = pack;
+                },
+                None => todo!(),
+            }
+        }
+        for pack in self.packs.iter() {
+            let (ref entries, _) = pack.subpacks[0];
+            for (key, value) in entries.iter() {
+                if let Some(entry) = field_map.get_mut(*key) {
+                    *entry = Some(value.clone());
+                }
+            }
+        }
+        visitor.visit_map(UnpackerFields {
+            unpacker: self,
+            fields: field_map.into_iter(),
+            value: None,
+        })
+    }
+    fn deserialize_enum<V>(self, _: &'static str, _: &'static [&'static str], _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_identifier<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_ignored_any<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+}
+
+impl<'pat, 'de> serde::Deserializer<'de> for Unpacker<'pat, 'de> {
+    type Error = QueryError;
+    fn deserialize_any<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_bool<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_i8<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_i16<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_i32<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_i64<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_u8<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_u16<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_u32<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_u64<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_f32<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_f64<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_char<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_str<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_string<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_bytes<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_byte_buf<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_option<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_unit<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_unit_struct<V>(self, _: &'static str, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_newtype_struct<V>(self, _: &'static str, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: serde::de::Visitor<'de>,
+    {
+        visitor.visit_seq(self)
+    }
+    fn deserialize_tuple<V>(self, _: usize, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_tuple_struct<V>(self, _: &'static str, _: usize, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_map<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_struct<V>(
+        self,
+        name: &'static str,
+        fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: serde::de::Visitor<'de>,
+    {
+        todo!()
+    }
+    fn deserialize_enum<V>(self, _: &'static str, _: &'static [&'static str], _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_identifier<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+    fn deserialize_ignored_any<V>(self, _: V) -> Result<V::Value, Self::Error> where V: serde::de::Visitor<'de> { todo!() }
+}
+
+//#[cfg(test)]
+//mod tests {
+//    use serde::Deserialize;
+//    use crate::vm::MAX_CALLS;
+//
+//    /// Mock struct for repo options.
+//    #[derive(Deserialize)]
+//    #[derive(Debug, PartialEq, Eq)]
+//    struct Options {
+//        active: bool,
+//        federate: Option<bool>,
+//        pinned: Option<bool>,
+//    }
+//
+//    /// Mock struct for a project branch.
+//    #[derive(Deserialize)]
+//    #[derive(Debug, PartialEq, Eq)]
+//    struct ProjectBranch {
+//        /// The project commit.
+//        commit: String,
+//        /// The URL to the repo.
+//        url: String,
+//        /// The relevant branch.
+//        branch: String,
+//        /// Branch options.
+//        options: Options,
+//    }
+//
+//    fn get_real_data() -> crate::vm::Pack<'static, 'static> {
+//        use indexmap::indexmap;
+//        use crate::vm::Pack;
+//        use crate::vm::SerdeObject;
+//        use crate::vm::SerdeObject::*;
+//
+//        fn mkstr<'a>(s: &'a str) -> SerdeObject<'a> {
+//            SerdeObject::Str(s.into())
+//        }
+//
+//        Pack {
+//            subpacks: vec![
+//                indexmap!{
+//                    "commit" => (
+//                        Pack {
+//                            subpacks: vec![
+//                                indexmap!{
+//                                    "url" => (
+//                                        Pack {
+//                                            subpacks: vec![
+//                                                indexmap!{
+//                                                    "branch" => (
+//                                                        Pack {
+//                                                            subpacks: vec![
+//                                                                indexmap!{
+//                                                                    "active" => (
+//                                                                        Pack {
+//                                                                            subpacks: vec![].into(),
+//                                                                        },
+//                                                                        Bool(
+//                                                                            true,
+//                                                                        ),
+//                                                                    ),
+//                                                                },
+//                                                            ].into(),
+//                                                        },
+//                                                        mkstr(
+//                                                            "HEAD",
+//                                                        ),
+//                                                    ),
+//                                                },
+//                                            ].into(),
+//                                        },
+//                                        mkstr(
+//                                            "https://github.com/ganarchy/GAnarchy",
+//                                        ),
+//                                    ),
+//                                },
+//                                indexmap!{
+//                                    "url" => (
+//                                        Pack {
+//                                            subpacks: vec![
+//                                                indexmap!{
+//                                                    "branch" => (
+//                                                        Pack {
+//                                                            subpacks: vec![
+//                                                                indexmap!{
+//                                                                    "pinned" => (
+//                                                                        Pack {
+//                                                                            subpacks: vec![].into(),
+//                                                                        },
+//                                                                        Bool(
+//                                                                            true,
+//                                                                        ),
+//                                                                    ),
+//                                                                    "active" => (
+//                                                                        Pack {
+//                                                                            subpacks: vec![].into(),
+//                                                                        },
+//                                                                        Bool(
+//                                                                            true,
+//                                                                        ),
+//                                                                    ),
+//                                                                },
+//                                                            ].into(),
+//                                                        },
+//                                                        mkstr(
+//                                                            "HEAD",
+//                                                        ),
+//                                                    ),
+//                                                },
+//                                            ].into(),
+//                                        },
+//                                        mkstr(
+//                                            "https://soniex2.autistic.space/git-repos/ganarchy.git",
+//                                        ),
+//                                    ),
+//                                },
+//                            ].into(),
+//                        },
+//                        mkstr(
+//                            "385e734a52e13949a7a5c71827f6de920dbfea43",
+//                        ),
+//                    ),
+//                },
+//                indexmap!{
+//                    "commit" => (
+//                        Pack {
+//                            subpacks: vec![
+//                                indexmap!{
+//                                    "url" => (
+//                                        Pack {
+//                                            subpacks: vec![
+//                                                indexmap!{
+//                                                    "branch" => (
+//                                                        Pack {
+//                                                            subpacks: vec![
+//                                                                indexmap!{
+//                                                                    "pinned" => (
+//                                                                        Pack {
+//                                                                            subpacks: vec![].into(),
+//                                                                        },
+//                                                                        Bool(
+//                                                                            true,
+//                                                                        ),
+//                                                                    ),
+//                                                                    "active" => (
+//                                                                        Pack {
+//                                                                            subpacks: vec![].into(),
+//                                                                        },
+//                                                                        Bool(
+//                                                                            true,
+//                                                                        ),
+//                                                                    ),
+//                                                                },
+//                                                            ].into(),
+//                                                        },
+//                                                        mkstr(
+//                                                            "HEAD",
+//                                                        ),
+//                                                    ),
+//                                                },
+//                                            ].into(),
+//                                        },
+//                                        mkstr(
+//                                            "https://soniex2.autistic.space/git-repos/mmorfc.git",
+//                                        ),
+//                                    ),
+//                                },
+//                            ].into(),
+//                        },
+//                        mkstr(
+//                            "a8fb5087f79eafe312db270082c052c427b208c2",
+//                        ),
+//                    ),
+//                },
+//                indexmap!{
+//                    "commit" => (
+//                        Pack {
+//                            subpacks: vec![
+//                                indexmap!{
+//                                    "url" => (
+//                                        Pack {
+//                                            subpacks: vec![
+//                                                indexmap!{
+//                                                    "branch" => (
+//                                                        Pack {
+//                                                            subpacks: vec![
+//                                                                indexmap!{
+//                                                                    "pinned" => (
+//                                                                        Pack {
+//                                                                            subpacks: vec![].into(),
+//                                                                        },
+//                                                                        Bool(
+//                                                                            true,
+//                                                                        ),
+//                                                                    ),
+//                                                                    "active" => (
+//                                                                        Pack {
+//                                                                            subpacks: vec![].into(),
+//                                                                        },
+//                                                                        Bool(
+//                                                                            true,
+//                                                                        ),
+//                                                                    ),
+//                                                                },
+//                                                            ].into(),
+//                                                        },
+//                                                        mkstr(
+//                                                            "HEAD",
+//                                                        ),
+//                                                    ),
+//                                                },
+//                                            ].into(),
+//                                        },
+//                                        mkstr(
+//                                            "https://soniex2.autistic.space/git-repos/chewstuff.git",
+//                                        ),
+//                                    ),
+//                                },
+//                            ].into(),
+//                        },
+//                        mkstr(
+//                            "2d0b363fe3179087de59d9ef4a2d14af21d89071",
+//                        ),
+//                    ),
+//                },
+//            ].into(),
+//        }
+//    }
+//
+//    #[test]
+//    fn to_vec_of_struct() {
+//        let der = super::Unpacker::new(get_real_data(), MAX_CALLS);
+//        let res: Vec<ProjectBranch> = Deserialize::deserialize(der).unwrap();
+//        assert_eq!(res, [
+//            ProjectBranch {
+//                commit: "385e734a52e13949a7a5c71827f6de920dbfea43".into(),
+//                url: "https://github.com/ganarchy/GAnarchy".into(),
+//                branch: "HEAD".into(),
+//                options: Options {
+//                    active: true,
+//                    federate: None,
+//                    pinned: None,
+//                },
+//            },
+//            ProjectBranch {
+//                commit: "385e734a52e13949a7a5c71827f6de920dbfea43".into(),
+//                url: "https://soniex2.autistic.space/git-repos/ganarchy.git".into(),
+//                branch: "HEAD".into(),
+//                options: Options {
+//                    active: true,
+//                    federate: None,
+//                    pinned: Some(true),
+//                },
+//            },
+//            ProjectBranch {
+//                commit: "a8fb5087f79eafe312db270082c052c427b208c2".into(),
+//                url: "https://soniex2.autistic.space/git-repos/mmorfc.git".into(),
+//                branch: "HEAD".into(),
+//                options: Options {
+//                    active: true,
+//                    federate: None,
+//                    pinned: Some(true),
+//                },
+//            },
+//            ProjectBranch {
+//                commit: "2d0b363fe3179087de59d9ef4a2d14af21d89071".into(),
+//                url: "https://soniex2.autistic.space/git-repos/chewstuff.git".into(),
+//                branch: "HEAD".into(),
+//                options: Options {
+//                    active: true,
+//                    federate: None,
+//                    pinned: Some(true),
+//                },
+//            },
+//        ]);
+//    }
+//}