ocaml/step2_eval.ml

   1 module Env =
   2   Map.Make (
   3     String
   4     (*(struct
   5        type t = Types.Symbol
   6        let compare (Types.Symbol a) (Types.Symbol b) = compare a b
   7     end)*)
   8     )
   9
  10 let num_fun f = Types.Fn
  11   (function
  12     | [(Types.Int a); (Types.Int b)] -> Types.Int (f a b)
  13     | _ -> raise (Invalid_argument "Numeric args required for this Mal builtin"))
  14
  15 let repl_env = ref (List.fold_left (fun a b -> b a) Env.empty
  16   [ Env.add "+" (num_fun ( + ));
  17     Env.add "-" (num_fun ( - ));
  18     Env.add "*" (num_fun ( * ));
  19     Env.add "/" (num_fun ( / )) ])
  20
  21 let rec eval_ast ast env =
  22   match ast with
  23     | Types.Symbol s ->
  24         (try Env.find s !env
  25          with Not_found -> raise (Invalid_argument ("Symbol '" ^ s ^ "' not found")))
  26     | Types.MalList xs -> Types.MalList (List.map (fun x -> eval x env) xs)
  27     | _ -> ast
  28 and eval ast env =
  29   let result = eval_ast ast env in
  30     match result with
  31       | Types.MalList ((Types.Fn f) :: args) -> (f args)
  32       | _ -> result
  33
  34 let read str = Reader.read_str str
  35 let print exp = Printer.pr_str exp true
  36 let rep str env = print (eval (read str) env)
  37
  38 let rec main =
  39   try
  40     while true do
  41       print_string "user> ";
  42       let line = read_line () in
  43         try
  44           print_endline (rep line repl_env);
  45         with End_of_file -> ()
  46          | Invalid_argument x ->
  47              output_string stderr ("Invalid_argument exception: " ^ x ^ "\n");
  48              flush stderr
  49     done
  50   with End_of_file -> ()