Seperate apply from eval

eval.ml

@@ -219,9 +219,9 @@ let binop op l r =
 
 exception Unbound of string
 
-(* TODO: refactor eval, split function into parts *)
 let rec eval env ast =
-  let rec aux = function
+  let aux = eval env in (* eval with current env *)
+  match ast with
     | Nothing -> Nop
     | Nint n -> Int n
     | Nfloat n -> Float n
@@ -241,36 +241,14 @@ let rec eval env ast =
 
     | Unary (op, v) -> unary op (aux v)
     | Binop (l, op, r) -> binop op (aux l) (aux r)
+
     | If (co, th, el) ->
       begin match aux co with
         | Bool true -> aux th
         | Bool false -> aux el
         | v -> raise @@ Type.Invalid (Value.typeof v)
       end
-
-    | Apply (v, args) ->
-      begin match aux v with
-        | Function (itself, var, e, env) as f ->
-          begin match args with
-            | [] -> f
-            | a::args ->
-              let env =
-                (* binding itself into env for recursion *)
-                Option.fold
-                  ~none: env ~some: (fun v -> Env.bind (v, f) env)
-                  itself
-                |> Env.bind (var, aux a)
-              in
-              eval env @@ Apply (e, args)
-          end
-        | External f ->
-          let args = List.map aux args in
-          External.apply f args
-        | v ->
-          if args = []
-          then v
-          else raise @@ Type.Invalid (Value.typeof v)
-      end
+    | Apply (v, args) -> apply v args env
 
     | Set_binop_pre (op, l) ->
       let l =
@@ -290,9 +268,32 @@ let rec eval env ast =
        | None -> String "left"
        | Some a -> String (Parser.assoc_to_string a))
     | _ -> failwith "Eval.eval"
-  in
-  aux ast
 
+(* apply args to result of expr *)
+and apply expr args env =
+  match eval env expr with
+  | Function (itself, var, e, env) as f ->
+    begin match args with
+      | [] -> f
+      | a::args ->
+        let value = eval env a in
+        let env = (* binding itself into env for recursion *)
+          itself
+          |> Option.fold
+            ~none: env
+            ~some: (fun n -> Env.bind (n, f) env)
+          |> Env.bind (var, value)
+        in
+        eval env @@ Apply (e, args)
+    end
+  | External f ->
+    let args = List.map (eval env) args in
+    External.apply f args
+  | v ->
+    if args = [] then v
+    else raise @@ Type.Invalid (Value.typeof v)
+
+(* toplevel for global let *)
 let eval_top env_ref ast =
   let var, v = match ast with
     | Let (var, Nfunction (arg, e)) -> (* named function *)