diff --git a/lib/env.ml b/lib/env.ml
index a494fab..f8b2b7e 100644
--- a/lib/env.ml
+++ b/lib/env.ml
@@ -1,17 +1,16 @@
 open Ast
 (* the type `environment` is defined in Ast *)
 
-
-let new_lexical env = 
+let new_lexical (env : environment) : environment = 
   let h = Hashtbl.create 16 in
   h :: env
 
-let set_local env s v =
+let set_local (env : environment) (s : string) (v : lisp_val) : unit =
   match env with
   | [] -> ()
   | e1 :: _ -> Hashtbl.replace e1 s v
 
-let rec update env s v =
+let rec update (env : environment) s v =
   match env with
   | [] -> ()
   | e1 :: erest ->
@@ -25,10 +24,10 @@ let rec get_root (env : environment) =
   | e :: [] -> e
   | _ :: t -> get_root t
 
-let set_global env s v =
+let set_global (env : environment) s v =
   Hashtbl.replace (get_root env) s v
 
-let copy env =
+let copy (env : environment) : environment =
   List.map Hashtbl.copy env
 
 
diff --git a/lib/eval.ml b/lib/eval.ml
index 48241ef..5fe1b04 100644
--- a/lib/eval.ml
+++ b/lib/eval.ml
@@ -43,35 +43,26 @@ and eval_body env body =
   | LCons (form, next) -> ignore (eval_one env form); eval_body env next
   | _ -> LNil
 
-and err s = raise (Invalid_argument s)
 and bind_args env = function
-  | LNil -> (function
-      | LNil -> ()
-      | _ -> err "cannot bind arguments")
-  | LSymbol s ->
-    (function
-      | v -> Env.set_local env s v; ())
-  | LCons (LSymbol hl, tl) -> (function
-      | LCons (ha, ta) -> 
-        Env.set_local env hl ha;
-        bind_args env tl ta;
-      | _ -> err "cannot bind arguments")
-  | _ -> fun _ -> err "bind_args"
-  
+  | (LNil, LNil) -> ()
+  | (LSymbol s, v) -> Env.set_local env s v
+  | (LCons (LSymbol hl, tl), LCons (ha, ta)) -> Env.set_local env hl ha; bind_args env (tl, ta)
+  | _ -> invalid_arg "cannot bind argument list for function"
+
 and eval_apply args = function
   | LLambda (e, l, b)
   | LFunction (_, e, l, b) ->
     let lexical_env = Env.new_lexical e in
-    bind_args lexical_env l args;
+    bind_args lexical_env (l, args);
     eval_body lexical_env b
   | LUnnamedMacro (e, l, b)
   | LMacro (_, e, l, b) ->
     let lexical_env = Env.new_lexical e in
-    bind_args lexical_env l args;
+    bind_args lexical_env (l, args);
     eval_body lexical_env b
   | v ->
-    err ("Non-macro non-function value passed to eval_apply "
-        ^ dbg_print_one v); LNil
+    invalid_arg ("Non-macro non-function value passed to eval_apply "
+        ^ dbg_print_one v)
     
 
 
@@ -90,8 +81,8 @@ and eval_call env func args =
   | v -> raise (Invalid_argument 
                   (Printf.sprintf "eval_apply: cannot call non-function object %s" (dbg_print_one v)))
 
-and (* This only creates a *local* binding, contained to the body given. *)
-  bind_local env = function
+ (* This only creates a *local* binding, contained to the body given. *)
+let bind_local env = function
   | LCons (LSymbol s, LCons (v, body)) ->
     let e = Env.new_lexical env in
     Env.set_local e s v;
@@ -99,14 +90,14 @@ and (* This only creates a *local* binding, contained to the body given. *)
   | _ -> invalid_arg "invalid argument to bind-local"
 
 (* special form that creates a global binding *)
-and lisp_define env = function
+let lisp_define env = function
   | LCons (LSymbol s, LCons (v, LNil)) ->
      let evaluated = eval_one env v in
      Env.set_global env s evaluated;
      evaluated
   | _ -> invalid_arg "invalid args to def"
 
-and lisp_if env = function
+let lisp_if env = function
   | LCons (cond, LCons (if_true, LNil)) ->
     (match eval_one env cond with
      | LNil -> LNil