From 00a0de44315111933e13a8529e5830cdca1db0f5 Mon Sep 17 00:00:00 2001
From: greg <greg.shuflin@protonmail.com>
Date: Sat, 23 Feb 2019 00:34:44 -0800
Subject: [PATCH] Add ena crate for unification

---
 schala-lang/language/Cargo.toml          |  1 +
 schala-lang/language/src/lib.rs          |  1 +
 schala-lang/language/src/typechecking.rs | 38 ++++++++++++++++++++----
 3 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/schala-lang/language/Cargo.toml b/schala-lang/language/Cargo.toml
index ea09ac1..a210754 100644
--- a/schala-lang/language/Cargo.toml
+++ b/schala-lang/language/Cargo.toml
@@ -10,6 +10,7 @@ take_mut = "0.1.3"
 maplit = "*"
 lazy_static = "0.2.8"
 failure = "0.1.2"
+ena = "0.11.0"
 
 
 schala-lang-codegen = { path = "../codegen" }
diff --git a/schala-lang/language/src/lib.rs b/schala-lang/language/src/lib.rs
index aaa26dc..24d75ef 100644
--- a/schala-lang/language/src/lib.rs
+++ b/schala-lang/language/src/lib.rs
@@ -17,6 +17,7 @@ extern crate schala_repl;
 extern crate schala_repl_codegen;
 #[macro_use]
 extern crate schala_lang_codegen;
+extern crate ena;
 
 use std::cell::RefCell;
 use std::rc::Rc;
diff --git a/schala-lang/language/src/typechecking.rs b/schala-lang/language/src/typechecking.rs
index e64ad05..d3edbb0 100644
--- a/schala-lang/language/src/typechecking.rs
+++ b/schala-lang/language/src/typechecking.rs
@@ -4,10 +4,16 @@ use std::rc::Rc;
 // -nope, ghc deliberately does typechecking before desugaring to core
 // cf. a history of haskell, peyton-jones
 
+use ena::unify::{UnifyKey, InPlaceUnificationTable, UnificationTable};
+
 use crate::ast::*;
 use crate::util::ScopeStack;
 use crate::builtin::{PrefixOp, BinOp};
 
+use std::collections::HashMap;
+use std::hash::Hash;
+
+
 #[derive(Debug, Clone, PartialEq)]
 pub struct TypeData {
   ty: Option<Type>
@@ -23,6 +29,7 @@ pub type TypeName = Rc<String>;
 
 pub struct TypeContext<'a> {
   variable_map: ScopeStack<'a, Rc<String>, Type>,
+  unification_table: InPlaceUnificationTable<TypeVar>,
   //evar_count: u32
 }
 
@@ -49,8 +56,15 @@ pub enum Type {
   }
 }
 
-#[derive(Debug, Clone, PartialEq)]
-pub struct TypeVar(String);
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct TypeVar(usize);
+
+impl UnifyKey for TypeVar {
+  type Value = ();
+  fn index(&self) -> u32 { self.0 as u32 }
+  fn from_index(u: u32) -> TypeVar { TypeVar(u as usize) }
+  fn tag() -> &'static str { "TypeVar" }
+}
 
 #[derive(Debug, Clone, PartialEq)]
 pub enum TypeConst {
@@ -190,6 +204,7 @@ impl<'a> TypeContext<'a> {
   pub fn new() -> TypeContext<'a> {
     TypeContext { 
       variable_map: ScopeStack::new(None),
+      unification_table: UnificationTable::new(),
       //evar_count: 0
     }
   }
@@ -315,6 +330,7 @@ impl<'a> TypeContext<'a> {
   }
 
   fn lambda(&mut self, params: &Vec<FormalParam>, type_anno: &Option<TypeIdentifier>, body: &Block) -> InferResult<Type> {
+
     Ok(ty!(Unit))
   }
 
@@ -336,10 +352,20 @@ impl<'a> TypeContext<'a> {
 
   fn unify(&mut self, t1: Type, t2: Type) -> InferResult<Type> {
     use self::Type::*;
-    Ok(match (t1, t2) {
-      (Const(ref c1), Const(ref c2)) if c1 == c2 => Const(c1.clone()), //choice of c1 is arbitrary I *think*
-      (a, b) => return TypeError::new(format!("{:?} and {:?} do not unify", a, b)),
-    })
+    use std::collections::hash_map::Entry;
+
+    match (t1, t2) {
+      (Const(ref c1), Const(ref c2)) if c1 == c2 => Ok(Const(c1.clone())), //choice of c1 is arbitrary I *think*
+      (Const(ref c1), Var(ref v2)) => {
+        //TODO flesh this out!
+        Ok(Const(c1.clone()))
+      },
+      (a @ Var(_), b @ Const(_)) => self.unify(b, a),
+      (Var(v1), Var(v2)) => {
+        panic!()
+      },
+      (a, b) => TypeError::new(format!("{:?} and {:?} do not unify", a, b)),
+    }
   }
 }