Added type annotations for the environment module to make things clearer, switched bind_args implementation with a simpler one.

.gitignore

@@ -1 +1,2 @@
 _build
+*~

lib/ast.ml

@@ -21,38 +21,11 @@ type lisp_val =
   | LMacro of string * environment * lisp_val * lisp_val
   | LUnnamedMacro of environment * lisp_val * lisp_val
   | LQuoted of lisp_val
+(* the environment type needs to be defined here, as it is mutually
+ recursive with lisp_val *)
 and environment = (string, lisp_val) Hashtbl.t list
 
 
-let env_set_local env s v =
-  match env with
-  | [] -> ()
-  | e1 :: _ -> Hashtbl.replace e1 s v
-
-let rec env_update env s v =
-  match env with
-  | [] -> ()
-  | e1 :: erest ->
-     match Hashtbl.find_opt e1 s with
-     | None -> env_update erest s v
-     | Some _ -> Hashtbl.replace e1 s v
-
-let env_new_lexical env = 
-  let h = Hashtbl.create 16 in
-  h :: env
-
-let rec env_root (env : environment) =
-  match env with
-  | [] -> raise (Invalid_argument "Empty environment passed to env_root!")
-  | e :: [] -> e
-  | _ :: t -> env_root t
-
-let env_set_global env s v =
-  Hashtbl.replace (env_root env) s v
-
-let env_copy env =
-  List.map Hashtbl.copy env
-
 let rec dbg_print_one v =
   let pf = Printf.sprintf in
   match v with

lib/env.ml

@@ -0,0 +1,33 @@
+open Ast
+(* the type `environment` is defined in Ast *)
+
+let new_lexical (env : environment) : environment = 
+  let h = Hashtbl.create 16 in
+  h :: env
+
+let set_local (env : environment) (s : string) (v : lisp_val) : unit =
+  match env with
+  | [] -> ()
+  | e1 :: _ -> Hashtbl.replace e1 s v
+
+let rec update (env : environment) s v =
+  match env with
+  | [] -> ()
+  | e1 :: erest ->
+     match Hashtbl.find_opt e1 s with
+     | None -> update erest s v
+     | Some _ -> Hashtbl.replace e1 s v
+
+let rec get_root (env : environment) =
+  match env with
+  | [] -> raise (Invalid_argument "Empty environment passed to env_root!")
+  | e :: [] -> e
+  | _ :: t -> get_root t
+
+let set_global (env : environment) s v =
+  Hashtbl.replace (get_root env) s v
+
+let copy (env : environment) : environment =
+  List.map Hashtbl.copy env
+
+

lib/eval.ml

@@ -5,11 +5,11 @@ open InterpreterStdlib;;
 let default_env: environment = [Hashtbl.create 1024];;
 
 let add_builtin s f =
-  env_set_global default_env s (LBuiltinFunction (s, f))
+  Env.set_global default_env s (LBuiltinFunction (s, f))
 let add_special s f =
-  env_set_global default_env s (LBuiltinSpecial (s, f))
+  Env.set_global default_env s (LBuiltinSpecial (s, f))
 
-let make_env () = [Hashtbl.copy (List.hd default_env)]
+let make_env () = Env.copy default_env
 
 (* the type annotations are unnecessary, but help constrain us from a
 potentially more general function here *)
@@ -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, LNil) -> ()
-      | LNil -> ()
+  | (LSymbol s, v) -> Env.set_local env s v
-      | _ -> err "cannot bind arguments")
+  | (LCons (LSymbol hl, tl), LCons (ha, ta)) -> Env.set_local env hl ha; bind_args env (tl, ta)
-  | LSymbol s ->
+  | _ -> invalid_arg "cannot bind argument list for function"
-    (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"
 
 and eval_apply args = function
   | LLambda (e, l, b)
   | LFunction (_, e, l, b) ->
-    let lexical_env = env_new_lexical e in
+    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
+    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 "
+    invalid_arg ("Non-macro non-function value passed to eval_apply "
-        ^ dbg_print_one v); LNil
+        ^ dbg_print_one v)
     
 
 
@@ -90,23 +81,23 @@ 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. *)
+ (* This only creates a *local* binding, contained to the body given. *)
-  bind_local env = function
+let bind_local env = function
   | LCons (LSymbol s, LCons (v, body)) ->
-    let e = env_new_lexical env in
+    let e = Env.new_lexical env in
-    env_set_local e s v;
+    Env.set_local e s v;
     eval_body e body
   | _ -> 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;
+     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

lib/interpreterStdlib.ml

@@ -50,7 +50,7 @@ let lisp_list _ vs = vs
 (* builtin function that updates an existing binding *)
 let lisp_set env = function
   | LCons (LSymbol s, LCons (v, LNil)) ->
-     env_update env s v;
+     Env.update env s v;
      v
   | _ -> invalid_arg "invalid args to set"