step 6 scaffolding

impls/sml/Makefile

@@ -1,4 +1,4 @@
-STEP_BINS = step0_repl step1_read_print step2_eval step3_env step4_if_fn_do
+STEP_BINS = step0_repl step1_read_print step2_eval step3_env step4_if_fn_do step6_file
 
 sml_MODE_DEFAULT = polyml
 sml_MODE_CONFIG  = .smlmode

impls/sml/step6_file.mlb

@@ -0,0 +1,12 @@
+local
+    $(SML_LIB)/basis/basis.mlb
+    util.sml
+    types.sml
+    printer.sml
+    reader.sml
+    env.sml
+    core.sml
+    step6_file.sml
+in
+    main.sml
+end

impls/sml/step6_file.sml

@@ -0,0 +1,68 @@
+fun read s =
+    readStr s
+
+fun eval e (LIST (SYMBOL "def!"::args)) = evalDef e args
+  | eval e (LIST (SYMBOL "do"::args))   = evalDo e args
+  | eval e (LIST (SYMBOL "if"::args))   = evalIf e args
+  | eval e (LIST (SYMBOL "let*"::args)) = (e, evalLet e args)
+  | eval e (LIST (SYMBOL "fn*"::args))  = (e, evalFn e args)
+  | eval e (LIST (a::args))             = (e, evalApply e (eval' e a) args)
+  | eval e (SYMBOL s)                   = (e, evalSymbol e s)
+  | eval e ast                          = (e, ast)
+
+and eval' e ast = (#2 o eval e) ast
+
+and evalDef e [SYMBOL s, ast] = let val v = eval' e ast in (def s v e, v) end
+  | evalDef _ _               = raise NotApplicable "def! needs a symbol and a form to evaluate"
+
+and evalLet e [LIST bs, ast] = eval' (bind bs e) ast
+  | evalLet _ _              = raise NotApplicable "let* needs a list of bindings and a form to evaluate"
+
+and evalDo e (x::xs) = foldl (fn (x, (e,_)) => eval e x) (eval e x) xs
+  | evalDo _ _       = raise NotApplicable "do needs at least one argument"
+
+and evalIf e [c,a,b] = eval e c |> (fn (e,c) => eval e (if truthy c then a else b))
+  | evalIf e [c,a]   = evalIf e [c,a,NIL]
+  | evalIf _ _       = raise NotApplicable "if needs two or three arguments"
+
+and evalFn c [(LIST binds),body] = CLOSURE (fn (e) => fn (exprs) => eval' (bind (interleave binds exprs) (wrap e c)) body)
+  | evalFn _ _                   = raise NotApplicable "fn* needs a list of bindings and a body"
+
+and evalApply e (CLOSURE (f)) args = f e (map (eval' e) args)
+  | evalApply e (FN f)        args = f (map (eval' e) args)
+  | evalApply _ x             args = raise NotApplicable (prStr x ^ " is not applicable on " ^ prStr (LIST args))
+
+and evalSymbol e s = valOrElse (lookup e s)
+                               (fn _ => raise NotDefined ("symbol '" ^ s ^ "' not found"))
+
+and bind (SYMBOL s::v::rest) e = def s (eval' e v) e |> bind rest
+  | bind []                  e = e
+  | bind _ _ = raise NotApplicable "bindings must be a list of symbol/form pairs"
+
+fun print f =
+    prStr f
+
+fun rep e s =
+    s |> read |> eval e |> (fn (e, v) => (e, print v))
+    handle Nothing           => (e, "")
+         | SyntaxError msg   => (e, "SYNTAX ERROR: " ^ msg)
+         | NotApplicable msg => (e, "CANNOT APPLY: " ^ msg)
+         | NotDefined msg    => (e, "NOT DEFINED: " ^ msg)
+
+val initEnv = ENV [] |> bind coreNs
+
+fun repl e =
+    let open TextIO
+    in (
+        print("user> ");
+        case inputLine(stdIn) of
+            SOME(line) =>
+                let val (e', s) = rep e line
+                    val _ = print(s ^ "\n")
+                in
+                    repl e'
+                end
+            | NONE => ()
+    ) end
+
+fun main () = repl initEnv