1 files changed, 32 insertions, 3 deletions
diff --git a/src/lib.rs b/src/lib.rs
index 9e84de1..f41b4c6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,12 +5,41 @@ mod vm;
 
 pub use pattern::Pattern;
 
-// TODO
+// TODO investigate if this should be PatternTypes: Default
+/// Defines the types and operations used for matching.
 pub trait PatternTypes {
     /// The value type.
     type Value;
-    type Iter;
+
+    /// The owned key type. May be uninhabited.
+    // TODO replace with GATs.
+    type Key;
+
+    /// Returns an iterator over key-value pairs contained within an item, or
+    /// None if this operation is unsupported for the given value.
+    fn pairs<'b>(
+        item: &'b Self::Value
+    ) -> Option<Box<dyn Iterator<Item=(&'b Self::Value, &'b Self::Value)> + 'b>> {
+        // TODO remove these default impls that only exist for testing purposes
+        let x = None;
+        Some(Box::new(x.into_iter()))
+    }
+
+    /// Returns an optional key-value pair keyed by the given key, or None if
+    /// this operation is unsupported for the given value.
+    fn get<'a, 'b>(
+        item: &'b Self::Value,
+        key: &'a str
+    ) -> Option<Option<(&'b Self::Value, &'b Self::Value)>> {
+        // TODO remove these default impls that only exist for testing purposes
+        Some(None)
+    }
+
+    /// Returns whether two values are the same/equivalent. This must provide
+    /// the same guarantees as PartialEq. In fact, this is a replacement for
+    /// PartialEq for cases where it's not possible to just use PartialEq.
+    fn matches(left: &Self::Value, right: &Self::Value) -> bool;
 }
 
 // TODO
-pub type Predicate<T> = dyn (Fn(&<T as PatternTypes>::Value) -> bool) + Send + Sync;
+type Predicate<T> = dyn (Fn(&<T as PatternTypes>::Value) -> bool) + Send + Sync;