Update docs and changelog

CHANGELOG.md

@@ -9,7 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - `Set` stdlib
 - `Option.force_msg`
 - Loading namespaces into the current scope (e.g. `using Pair`)
-- Assign patterns to variables
+- Assign patterns to variables (e.g. `let x::(t = y::_) = [1, 2, 3, 4]` where `t == [2, 3, 4]`)
 ### Changed
 ### Removed
 

docs/sophia_features.md

@@ -471,6 +471,17 @@ function
   get_left(Both(x, _)) = Some(x)
 ```
 
+Sophia also supports the assignment of patterns to variables:
+```sophia
+function f(x) = switch(x)
+  h1::(t = h2::_) => (h1 + h2)::t  // same as `h1::h2::k => (h1 + h2)::h2::k`
+  _ => x
+
+function g(p : int * option(int)) : int =
+  let (a, (o = Some(b))) = p  // o is equal to Pair.snd(p)
+  b
+```
+
 *NOTE: Data types cannot currently be recursive.*
 
 ## Lists