mirror of
https://github.com/kanaka/mal.git
synced 2024-10-26 22:28:26 +03:00
78 lines
2.6 KiB
Standard ML
78 lines
2.6 KiB
Standard ML
exception NotDefined of string
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exception NotApplicable of string
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fun read s =
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readStr s
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fun eval e (LIST (SYMBOL "def!"::args)) = evalDef e args
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| eval e (LIST (SYMBOL "let*"::args)) = evalLet e args
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| eval e (LIST (a::args)) = evalApply e (eval e a) args
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| eval e (SYMBOL s) = evalSymbol e s
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| eval e ast = ast
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and evalDef e [SYMBOL s, ast] = let val v = eval e ast in (def s v e; v) end
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| evalDef _ _ = raise NotApplicable "def! needs a symbol and a form to evaluate"
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and evalLet e [LIST bs, ast] = eval (bind bs (inside e)) ast
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| evalLet _ _ = raise NotApplicable "let* needs a list of bindings and a form to evaluate"
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and evalApply e (FN f) args = f (map (eval e) args)
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| evalApply _ a args = raise NotApplicable (prStr a ^ " is not applicable on " ^ prStr (LIST args))
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and evalSymbol e s = valOrElse (lookup e s)
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(fn _ => raise NotDefined ("symbol '" ^ s ^ "' not found"))
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and bind (SYMBOL s::v::rest) e = (def s (eval e v) e; bind rest e)
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| bind [] e = e
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| bind _ _ = raise NotApplicable "bindings must be a list of symbol/form pairs"
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fun print f =
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prStr f
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fun rep e s =
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s |> read |> eval e |> print
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handle Nothing => ""
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| SyntaxError msg => "SYNTAX ERROR: " ^ msg
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| NotApplicable msg => "CANNOT APPLY: " ^ msg
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| NotDefined msg => "NOT DEFINED: " ^ msg
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fun malPlus (INT a, INT b) = INT (a + b)
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| malPlus _ = raise NotApplicable "can only add integers"
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fun malTimes (INT a, INT b) = INT (a * b)
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| malTimes _ = raise NotApplicable "can only multiply integers"
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fun malMinus (INT b, INT a) = INT (a - b)
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| malMinus _ = raise NotApplicable "can only subtract integers"
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fun malDiv (INT b, INT a) = INT (a div b)
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| malDiv _ = raise NotApplicable "can only divide integers"
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val initEnv = ENV (NS (ref [])) |> bind [
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SYMBOL "+",
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FN (foldl malPlus (INT 0)),
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SYMBOL "*",
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FN (foldl malTimes (INT 1)),
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SYMBOL "-",
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FN (fn [x] => malMinus (x, INT 0)
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| x::xs => foldr malMinus x xs
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| _ => raise NotApplicable "'-' requires arguments"),
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SYMBOL "/",
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FN (fn [x] => malDiv (x, INT 1)
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| x::xs => foldr malDiv x xs
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| _ => raise NotApplicable "'/' requires arguments")
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]
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fun repl e =
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let open TextIO
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in (
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print("user> ");
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case inputLine(stdIn) of
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SOME(line) =>
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let val s = rep e line
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val _ = print(s ^ "\n")
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in
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repl e
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end
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| NONE => ()
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) end
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fun main () = repl initEnv
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