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step 6 scaffolding
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STEP_BINS = step0_repl step1_read_print step2_eval step3_env step4_if_fn_do
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STEP_BINS = step0_repl step1_read_print step2_eval step3_env step4_if_fn_do step6_file
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sml_MODE_DEFAULT = polyml
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sml_MODE_CONFIG = .smlmode
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12
impls/sml/step6_file.mlb
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12
impls/sml/step6_file.mlb
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local
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$(SML_LIB)/basis/basis.mlb
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util.sml
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types.sml
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printer.sml
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reader.sml
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env.sml
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core.sml
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step6_file.sml
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in
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main.sml
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end
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68
impls/sml/step6_file.sml
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68
impls/sml/step6_file.sml
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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 "do"::args)) = evalDo e args
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| eval e (LIST (SYMBOL "if"::args)) = evalIf e args
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| eval e (LIST (SYMBOL "let*"::args)) = (e, evalLet e args)
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| eval e (LIST (SYMBOL "fn*"::args)) = (e, evalFn e args)
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| eval e (LIST (a::args)) = (e, evalApply e (eval' e a) args)
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| eval e (SYMBOL s) = (e, evalSymbol e s)
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| eval e ast = (e, ast)
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and eval' e ast = (#2 o eval e) 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 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 evalDo e (x::xs) = foldl (fn (x, (e,_)) => eval e x) (eval e x) xs
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| evalDo _ _ = raise NotApplicable "do needs at least one argument"
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and evalIf e [c,a,b] = eval e c |> (fn (e,c) => eval e (if truthy c then a else b))
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| evalIf e [c,a] = evalIf e [c,a,NIL]
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| evalIf _ _ = raise NotApplicable "if needs two or three arguments"
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and evalFn c [(LIST binds),body] = CLOSURE (fn (e) => fn (exprs) => eval' (bind (interleave binds exprs) (wrap e c)) body)
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| evalFn _ _ = raise NotApplicable "fn* needs a list of bindings and a body"
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and evalApply e (CLOSURE (f)) args = f e (map (eval' e) args)
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| evalApply e (FN f) args = f (map (eval' e) args)
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| evalApply _ x args = raise NotApplicable (prStr x ^ " 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
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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 |> (fn (e, v) => (e, print v))
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handle Nothing => (e, "")
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| SyntaxError msg => (e, "SYNTAX ERROR: " ^ msg)
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| NotApplicable msg => (e, "CANNOT APPLY: " ^ msg)
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| NotDefined msg => (e, "NOT DEFINED: " ^ msg)
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val initEnv = ENV [] |> bind coreNs
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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 (e', 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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