From e501f4bd104e19144822401d00c61edc50e61b45 Mon Sep 17 00:00:00 2001
From: greg <greg.shuflin@protonmail.com>
Date: Sat, 23 Feb 2019 09:58:44 -0800
Subject: [PATCH] Various cleanup of comments, stringifying types

---
 schala-lang/language/src/typechecking.rs | 69 ++++++++++++++++--------
 1 file changed, 47 insertions(+), 22 deletions(-)

diff --git a/schala-lang/language/src/typechecking.rs b/schala-lang/language/src/typechecking.rs
index 7d17108..266dce1 100644
--- a/schala-lang/language/src/typechecking.rs
+++ b/schala-lang/language/src/typechecking.rs
@@ -1,8 +1,5 @@
 use std::rc::Rc;
-//THINGS TODO
-// look at the haskell compiler, see where in its flow the typechecking happens
-// -nope, ghc deliberately does typechecking before desugaring to core
-// cf. a history of haskell, peyton-jones
+use std::fmt::Write;
 
 use ena::unify::{UnifyKey, InPlaceUnificationTable, UnificationTable, EqUnifyValue};
 
@@ -10,9 +7,6 @@ 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 {
@@ -40,7 +34,7 @@ type InferResult<T> = Result<T, TypeError>;
 pub struct TypeError { pub msg: String }
 
 impl TypeError {
-  fn new<A, T>(msg: T) -> InferResult<A> where T: Into<String> { //TODO make these kinds of error-producing functions CoW-ready
+  fn new<A, T>(msg: T) -> InferResult<A> where T: Into<String> {
     Err(TypeError { msg: msg.into() })
   }
 }
@@ -81,28 +75,56 @@ pub enum TypeConst {
   UserDefined
 }
 
+impl TypeConst {
+  pub fn to_string(&self) -> String {
+    use self::TypeConst::*;
+    match self {
+      Unit => format!("()"),
+      Nat => format!("Nat"),
+      Int => format!("Int"),
+      Float => format!("Float"),
+      StringT => format!("String"),
+      Bool => format!("Bool"),
+      Ordering => format!("Ordering"),
+      _ => format!("UNKNOWN TYPE"),
+    }
+  }
+}
+
 impl EqUnifyValue for TypeConst { }
 
 macro_rules! ty {
   ($type_name:ident) => { Type::Const(TypeConst::$type_name) };
   ($t1:ident -> $t2:ident) => { Type::Arrow { params: vec![ty!($t1)], ret: box ty!($t2) } };
   ($t1:ident -> $t2:ident -> $t3:ident) => { Type::Arrow { params: vec![ty!($t1), ty!($t2)], ret: box ty!($t3) } };
+  ($type_list:ident, $ret_type:ident) => {
+    Type::Arrow {
+      params: $type_list,
+      ret: box $ret_type,
+    }
+  }
 }
 
 //TODO find a better way to capture the to/from string logic
 impl Type {
   pub fn to_string(&self) -> String {
     use self::Type::*;
-    use self::TypeConst::*;
     match self {
-      Const(Unit) => format!("()"),
-      Const(Nat) => format!("Nat"),
-      Const(Int) => format!("Int"),
-      Const(Float) => format!("Float"),
-      Const(StringT) => format!("String"),
-      Const(Bool) => format!("Bool"),
-      Const(Ordering) => format!("Ordering"),
-      _ => format!("UNKNOWN TYPE"),
+      Const(c) => c.to_string(),
+      Var(v) => format!("t_{}", v.0),
+      Arrow { params, box ref ret } => {
+        if params.len() == 0 {
+          format!("-> {}", ret.to_string())
+        } else {
+          let mut buf = String::new();
+          for p in params.iter() {
+            write!(buf, "{} -> ", p.to_string());
+          }
+          write!(buf, "{}", ret.to_string());
+          buf
+        }
+      },
+      Compound { .. } => format!("<some compound type>")
     }
   }
 
@@ -228,6 +250,9 @@ impl<'a> TypeContext<'a> {
 
   }
 
+  /// `typecheck` is the entry into the type-inference system, accepting an AST as an argument
+  /// Following the example of GHC, the compiler deliberately does typechecking before de-sugaring
+  /// the AST to ReducedAST
   pub fn typecheck(&mut self, ast: &AST) -> Result<Type, TypeError> {
     let mut returned_type = Type::Const(TypeConst::Unit);
     for statement in ast.0.iter() {
@@ -334,11 +359,12 @@ impl<'a> TypeContext<'a> {
       }
     }).collect();
     let argument_types = argument_types?;
+    let ret_type = match type_anno.as_ref() {
+      Some(anno) => self.get_type_from_name(anno)?,
+      None => Type::Var(self.fresh_type_variable())
+    };
 
-    println!("ARGUMENT TYPES: {:?}", argument_types);
-
-    //TODO finish this
-    Ok(ty!(UserDefined))
+    Ok(ty!(argument_types, ret_type))
   }
 
   fn call(&mut self, f: &Expression, args: &Vec<Meta<Expression>>) -> InferResult<Type> {
@@ -379,7 +405,6 @@ impl<'a> TypeContext<'a> {
 
   fn unify(&mut self, t1: Type, t2: Type) -> InferResult<Type> {
     use self::Type::*;
-    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*