env cons-list instead of tree structure

lib/compile/ir.ml

@@ -64,27 +64,33 @@ and lambda = {
 
 module Env = struct
   type t =
+    | Empty
     | Obj of {
+        pred : t;
         self : id;
         elems : (string, string) Hashtbl.t;
       }
     | Fun of {
+        pred : t;
         args : (string * id) list;
         (* clos : ??? *)
       }
-    | Cons of t * t
 
   let rec find name = function
-    | Fun { args } ->
-      (* TODO: closure conversion *)
-      List.assoc name args, None
+    | Empty ->
+      raise Not_found
 
-    | Obj { self; elems } ->
-      self, Some (Hashtbl.find elems name)
+    | Fun { pred; args } ->
+      begin match List.assoc name args with
+        | id -> id, None
+        | exception Not_found -> find name pred
+      end
 
-    | Cons (e1, e2) ->
-      try find name e1 with
-        Not_found -> find name e2
+    | Obj { pred; self; elems } ->
+      begin match Hashtbl.find elems name with
+        | elem -> self, Some elem
+        | exception Not_found -> find name pred
+      end
 end
 
 let seq_r a b = Seq (b, a)
@@ -179,8 +185,8 @@ let lower ~lib (modl : Ast.modl) =
       compile_error "scope does not end in expression";
 
     let self = new_id "obj" in
-    let env' = Env.Obj { self; elems } in
-    let env = Env.Cons (env', env) in
+    let env = Env.Obj { self; elems; pred = env } in
+    let env' = Env.Obj { self; elems; pred = Empty } in
 
     let funs_r, vals_r, inits_r =
       List.fold_left
@@ -228,7 +234,7 @@ let lower ~lib (modl : Ast.modl) =
 
   and lower_lambda self env args body =
     let args = List.map (fun a -> a, new_id a) args in
-    let env = Env.Cons (Fun { args }, env) in
+    let env = Env.Fun { args; pred = env } in
     (* TODO: closure conversion *)
     let body = lower_exp env body in
     let args = List.map snd args in
@@ -239,7 +245,7 @@ let lower ~lib (modl : Ast.modl) =
   let self = new_id "lib" in
   let elems = Hashtbl.create 128 in
   List.iter (fun (name, _) -> Hashtbl.add elems name name) lib;
-  let env = Env.Obj { self; elems } in
+  let env = Env.Obj { self; elems; pred = Empty } in
   let args = [] in
   let body = lower_block env modl.items in
   { self; args; body }