From e6908a66ecabaca6e7adf4e847afe228f5d9f257 Mon Sep 17 00:00:00 2001
From: Patrick Walton <pcwalton@mimiga.net>
Date: Thu, 16 Dec 2010 11:11:48 -0800
Subject: [PATCH] rustc: Infer the types of type-parametric functions

---
 src/comp/middle/typeck.rs | 76 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/src/comp/middle/typeck.rs b/src/comp/middle/typeck.rs
index 9837ffa1add..332c893e841 100644
--- a/src/comp/middle/typeck.rs
+++ b/src/comp/middle/typeck.rs
@@ -259,6 +259,79 @@ fn ty_to_str(&@ty typ) -> str {
     ret s;
 }
 
+// Replaces parameter types inside a type with type variables.
+fn generalize_ty(@crate_ctxt cx, @ty t) -> @ty {
+    fn rewrap(@ty orig, &sty new) -> @ty {
+        ret @rec(struct=new, mut=orig.mut, cname=orig.cname);
+    }
+
+    fn recur(@crate_ctxt cx, @ty t,
+             &hashmap[ast.def_id,@ty] ty_params_to_ty_vars) -> @ty {
+        alt (t.struct) {
+            case (ty_box(?subty)) {
+                auto new_subty = recur(cx, subty, ty_params_to_ty_vars);
+                ret rewrap(t, ty_box(new_subty));
+            }
+            case (ty_vec(?subty)) {
+                auto new_subty = recur(cx, subty, ty_params_to_ty_vars);
+                ret rewrap(t, ty_vec(new_subty));
+            }
+            case (ty_tup(?subtys)) {
+                let vec[@ty] new_subtys = vec();
+                for (@ty subty in subtys) {
+                    new_subtys += vec(recur(cx, subty, ty_params_to_ty_vars));
+                }
+                ret rewrap(t, ty_tup(new_subtys));
+            }
+            case (ty_rec(?fields)) {
+                let vec[field] new_fields = vec();
+                for (field fld in fields) {
+                    auto new_ty = recur(cx, fld.ty, ty_params_to_ty_vars);
+                    new_fields += vec(rec(ident=fld.ident, ty=new_ty));
+                }
+                ret rewrap(t, ty_rec(new_fields));
+            }
+            case (ty_fn(?args, ?ret_ty)) {
+                let vec[arg] new_args = vec();
+                for (arg a in args) {
+                    auto new_ty = recur(cx, a.ty, ty_params_to_ty_vars);
+                    new_args += vec(rec(mode=a.mode, ty=new_ty));
+                }
+                auto new_ret_ty = recur(cx, ret_ty, ty_params_to_ty_vars);
+                ret rewrap(t, ty_fn(new_args, new_ret_ty));
+            }
+            case (ty_obj(?methods)) {
+                let vec[method] new_methods = vec();
+                for (method m in methods) {
+                    let vec[arg] new_args = vec();
+                    for (arg a in m.inputs) {
+                        auto new_ty = recur(cx, a.ty, ty_params_to_ty_vars);
+                        new_args += vec(rec(mode=a.mode, ty=new_ty));
+                    }
+                    auto new_rty = recur(cx, m.output, ty_params_to_ty_vars);
+                    new_methods += vec(rec(ident=m.ident, inputs=new_args,
+                                           output=new_rty));
+                }
+                ret rewrap(t, ty_obj(new_methods));
+            }
+            case (ty_param(?pid)) {
+                if (ty_params_to_ty_vars.contains_key(pid)) {
+                    ret ty_params_to_ty_vars.get(pid);
+                }
+                auto var_ty = next_ty_var(cx);
+                ty_params_to_ty_vars.insert(pid, var_ty);
+                ret var_ty;
+            }
+            case (_) { /* fall through */ }
+        }
+
+        ret t;
+    }
+
+    auto ty_params_to_ty_vars = common.new_def_hash[@ty]();
+    ret recur(cx, t, ty_params_to_ty_vars);
+}
+
 // Parses the programmer's textual representation of a type into our internal
 // notion of a type. `getter` is a function that returns the type
 // corresponding to a definition ID.
@@ -1720,6 +1793,9 @@ fn check_expr(&fn_ctxt fcx, @ast.expr expr) -> @ast.expr {
                     fail;
                 }
             }
+
+            t = generalize_ty(fcx.ccx, t); 
+
             ret @fold.respan[ast.expr_](expr.span,
                                         ast.expr_name(name, defopt,
                                                       ast.ann_type(t)));