430 lines
15 KiB
Racket
430 lines
15 KiB
Racket
;;; ---<<<TOY>>>----------------------------------------------------
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#lang pl
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;;; ----------------------------------------------------------------
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;;; Syntax
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#| The AST:
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<TOY> ::= <num>
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| <id>
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| { bind {{ <id> <TOY> } ... } <TOY> ... }
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| { bindrec {{ <id> <TOY> } ... } <TOY> ... }
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| { fun { <id> ... } <TOY> ... }
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| { rfun { <id> ... } <TOY> ... }
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| { <TOY> <TOY> ... }
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| { if <TOY> <TOY> <TOY> }
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| { set! <id> <TOY> }
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|#
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;; A matching abstract syntax tree datatype:
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(define-type TOY
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[Num Number]
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[Id Symbol]
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[Bind (Listof Symbol) (Listof TOY) (Listof TOY)]
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[Bindrec (Listof Symbol) (Listof TOY) (Listof TOY)]
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[Fun (Listof Symbol) (Listof TOY)]
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[Rfun (Listof Symbol) (Listof TOY)]
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[Call TOY (Listof TOY)]
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[If TOY TOY TOY]
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[Set Symbol TOY])
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; Things you can't name things.
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(define BAD_WORDS (list 'bind 'bindrec 'fun 'rfun 'if 'set! '+ '- '* '/ '= '< '> 'true 'false 'void))
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(: unique-list? : (Listof Any) -> Boolean)
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;; Tests whether a list is unique, guards Bind and Fun values.
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(define (unique-list? xs)
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(or (null? xs)
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(and (not (member (first xs) (rest xs)))
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(unique-list? (rest xs)))))
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(: no-bad-words? : (Listof Symbol) -> Boolean)
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;; Tests whether a list avoids all bad words.
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(define (no-bad-words? names)
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(or (null? names)
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(and (not (member (first names) BAD_WORDS))
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(no-bad-words? (rest names)))))
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(: parse-sexpr : Sexpr -> TOY)
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;; parses s-expressions into TOYs
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(define (parse-sexpr sexpr)
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(match sexpr
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; Primitives.
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[(number: n) (Num n)]
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[(symbol: name) (Id name)]
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; Bindrec.
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[(cons (and binder (or 'bind 'bindrec)) _) ; `binder` bound to 'bind or 'bindrec.
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; `_` feels cooler than `more`.
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(match sexpr
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[(list b (list (list (symbol: names) (sexpr: nameds)) ...) body ...)
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(if (not (null? body))
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(if (unique-list? names)
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(if (no-bad-words? names)
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((if (symbol=? b 'bind) Bind Bindrec)
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names
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(map parse-sexpr nameds)
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(map parse-sexpr body))
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(error 'parse-sexpr "bad word found in `~s' : ~s" binder names))
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(error 'parse-sexpr "duplicate `~s' names: ~s" binder names))
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(error 'parse-sexpr "bind expression missing body: ~s" sexpr))]
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[else (error 'parse-sexpr "bad `~s' syntax in ~s" binder sexpr)])]
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;
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;
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;
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; RFun definition.
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[(cons (and funer (or 'fun 'rfun)) _)
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(match sexpr
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[(list f (list (symbol: parameters) ...) body ...)
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(if (not (null? body))
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(if (unique-list? parameters)
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(if (no-bad-words? parameters)
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((if (symbol=? f 'fun) Fun Rfun) parameters (map parse-sexpr body))
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(error 'parse-sexpr "bad words found in function parameter names in ~s" sexpr))
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(error 'parse-sexpr "bad parameters defined for function in ~s" sexpr))
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(error 'parse-sexpr "disemobodied function in ~s" sexpr))]
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[else (error 'parse-sexpr "bad function syntax in ~s" sexpr)])]
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; Conditional.
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[(cons 'if _)
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(match sexpr
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[(list 'if cond then else)
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(If (parse-sexpr cond)
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(parse-sexpr then)
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(parse-sexpr else))]
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[else (error 'parse-sexpr "bad `if' syntax in ~s" sexpr)])]
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; Set!.
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[(cons 'set! _)
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(match sexpr
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[(list 'set! (symbol: thing) as)
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(Set thing (parse-sexpr as))])]
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; Function application
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[(list fun args ...) ; other lists are applications
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(Call (parse-sexpr fun)
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(map parse-sexpr args))]
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; Bad.
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[else (error 'parse-sexpr "bad syntax in ~s" sexpr)]))
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(: parse : String -> TOY)
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;; Parses a string containing an TOY expression to a TOY AST.
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(define (parse str)
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(parse-sexpr (string->sexpr str)))
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(define-type ENV
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[EmptyEnv]
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[FrameEnv FRAME ENV])
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;; a frame is an association list of names and values.
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(define-type FRAME = (Listof (List Symbol (Boxof VAL))))
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(define-type VAL
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[RktV Any]
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; Parameters, compiled body, whether it's an Rfun, environment.
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[FunV (Listof Symbol) (ENV -> VAL) Boolean ENV]
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[PrimV ((Listof VAL) -> VAL)]
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[VoidV])
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(: extend : (Listof Symbol) (Listof VAL) ENV -> ENV)
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(define (extend names vals env)
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(raw-extend names (map (inst box VAL) vals) env))
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(: raw-extend : (Listof Symbol) (Listof (Boxof VAL)) ENV -> ENV)
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;; extends an environment with a new frame.
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(define (raw-extend names bvals env)
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(if (= (length names) (length bvals))
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(FrameEnv (map (lambda ([name : Symbol] [bval : (Boxof VAL)])
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(list name bval))
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names bvals)
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env)
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(error 'extend "arity mismatch for names: ~s" names)))
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(: extend-rec : (Listof Symbol) (Listof (ENV -> VAL)) ENV -> ENV)
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(define (extend-rec names compiled-vals env)
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(define newenv (extend names (map (lambda (_) (VoidV)) compiled-vals) env))
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(for-each (lambda ([name : Symbol] [compiled-val : (ENV -> VAL)])
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(set-box! (lookup name newenv) (compiled-val newenv)))
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names compiled-vals)
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newenv)
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(: lookup : Symbol ENV -> (Boxof VAL))
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;; lookup a symbol in an environment, frame by frame,
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;; return its value or throw an error if it isn't bound
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(define (lookup name env)
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(cases env
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[(EmptyEnv) (error 'lookup "no binding for ~s" name)]
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[(FrameEnv frame rest)
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(let ([cell (assq name frame)])
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(if cell
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(second cell)
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(lookup name rest)))]))
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(: unwrap-rktv : VAL -> Any)
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;; helper for `racket-func->prim-val': unwrap a RktV wrapper in
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;; preparation to be sent to the primitive function
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(define (unwrap-rktv x)
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(cases x
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[(RktV v) v]
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[else (error 'racket-func "bad input: ~s" x)]))
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(: racket-func->prim-val : Function -> (Boxof VAL))
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;; converts a racket function to a primitive evaluator function
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;; which is a PrimV holding a ((Listof VAL) -> VAL) function.
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;; (the resulting function will use the list function as is,
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;; and it is the list function's responsibility to throw an error
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;; if it's given a bad number of arguments or bad input types.)
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(define (racket-func->prim-val racket-func)
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(define list-func (make-untyped-list-function racket-func))
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(box (PrimV (lambda (args)
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(RktV (list-func (map unwrap-rktv args)))))))
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;; The global environment has a few primitives:
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(: global-environment : ENV)
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(define global-environment
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(FrameEnv (list (list '+ (racket-func->prim-val +))
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(list '- (racket-func->prim-val -))
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(list '* (racket-func->prim-val *))
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(list '/ (racket-func->prim-val /))
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(list '< (racket-func->prim-val <))
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(list '> (racket-func->prim-val >))
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(list '= (racket-func->prim-val =))
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;; values
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(list 'true (box (RktV #t)))
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(list 'false (box (RktV #f)))
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(list 'void (box (VoidV))))
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(EmptyEnv)))
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(: compiler-enabled? : (Boxof Boolean))
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(define compiler-enabled? (box #f))
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(: ensure-compiler-enabled! : Symbol -> Void)
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(define (ensure-compiler-enabled! who)
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(if (unbox compiler-enabled?)
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(void)
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(error who "compiler is not enabled")))
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(: run-compiled-body : (Listof (ENV -> VAL)) ENV -> VAL)
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; Compile a body of expressions.
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(define (run-compiled-body compiled env)
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(if (null? compiled)
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(error 'compile "empty body")
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(if (null? (rest compiled))
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((first compiled) env)
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(let ([_ ((first compiled) env)]) ; We've side effects in this language.
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(run-compiled-body (rest compiled) env)))))
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(: compile-body : (Listof TOY) -> (ENV -> VAL))
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;; Compile a sequence of body expressions into runtime sequencing code.
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(define (compile-body body)
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(ensure-compiler-enabled! 'compile-body)
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(define compiled-body (map compile body))
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(lambda ([env : ENV])
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(run-compiled-body compiled-body env)))
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; Convenient helper for running compiled code.
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(: caller : ENV -> (ENV -> VAL) -> VAL)
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(define (caller env)
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(lambda ([compiled : (ENV -> VAL)]) (compiled env)))
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(: compile : TOY -> (ENV -> VAL))
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;; compileuates TOY expressions.
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(define (compile expr)
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(ensure-compiler-enabled! 'compile)
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(cases expr
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[(Num n) (λ ([_ : ENV]) (RktV n))]
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[(Id name) (λ ([env : ENV]) (unbox (lookup name env)))]
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[(Bind names exprs body)
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(define compiled-exprs (map compile exprs))
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(define compiled-body (compile-body body))
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(λ ([env : ENV])
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(compiled-body
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(extend names
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(map (caller env) compiled-exprs)
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env)))]
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[(Bindrec names exprs body)
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(define compiled-exprs (map compile exprs))
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(define compiled-body (compile-body body))
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(λ ([env : ENV])
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(compiled-body (extend-rec names compiled-exprs env)))]
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[(Fun names body)
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(define compiled-body (compile-body body))
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(λ ([env : ENV]) (FunV names compiled-body #f env))]
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[(Rfun names body)
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(define compiled-body (compile-body body))
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(λ ([env : ENV]) (FunV names compiled-body #t env))]
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[(Call fun-expr arg-exprs)
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(define compiled-fun (compile fun-expr))
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(define compiled-args (map compile arg-exprs))
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(define compiled-get-boxes (compile-get-boxes arg-exprs))
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(λ ([env : ENV])
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(let ([fval (compiled-fun env)]
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[arg-vals-thunk
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(lambda ()
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(map (caller env) compiled-args))]) ; THunk.
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(cases fval
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[(PrimV proc) (proc (arg-vals-thunk))]
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[(FunV names body ref? fun-env)
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(if ref?
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(compile-rfun names compiled-get-boxes body env fun-env)
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(body (extend names (arg-vals-thunk) fun-env)))]
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[else (error 'compile "function call with a non-function: ~s"
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fval)])))]
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[(If cond-expr then-expr else-expr)
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(define compiled-cond (compile cond-expr))
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(define compiled-then (compile then-expr))
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(define compiled-else (compile else-expr))
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(λ ([env : ENV])
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(if (cases (compiled-cond env)
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[(RktV v) v] ; Racket value => use as boolean
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[else #t]) ; other values are always true
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(compiled-then env)
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(compiled-else env)))]
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[(Set thing as)
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(define compiled-as (compile as))
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(λ ([env : ENV])
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(set-box! (lookup thing env) (compiled-as env))
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(VoidV))]))
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(: compile-rfun : (Listof Symbol) (ENV -> (Listof (Boxof VAL))) (ENV -> VAL) ENV ENV -> VAL)
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; Compile an RFun.
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(define (compile-rfun params get-boxes body callerenv calleeenv)
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(body (raw-extend params (get-boxes callerenv) calleeenv)))
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(: compile-get-boxes : (Listof TOY) -> (ENV -> (Listof (Boxof VAL))))
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; Utility for applying rfun.
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(define (compile-get-boxes exprs)
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(ensure-compiler-enabled! 'compile-get-boxes)
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(: compile-getter : TOY -> (ENV -> (Boxof VAL)))
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(define (compile-getter expr)
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(cases expr
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[(Id name) (lambda ([env : ENV]) (lookup name env))]
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[else
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(lambda ([_ : ENV]) (error 'compile-get-boxes "non-identifier"))]))
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(let ([getters (map compile-getter exprs)])
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(lambda ([env : ENV])
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(map (lambda ([getter : (ENV -> (Boxof VAL))])
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(getter env))
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getters))))
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(: run : String -> Any)
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;; evaluate a TOY program contained in a string
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(define (run str)
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(define parsed (parse str))
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(set-box! compiler-enabled? #t)
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(define compiled (compile parsed))
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(set-box! compiler-enabled? #f)
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(let ([result (compiled global-environment)])
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(cases result
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[(RktV v) v]
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[else (error 'run "evaluation returned a bad value: ~s"
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result)])))
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(test (run "{{rfun {x} x} {/ 4 0}}") =error> "non-identifier")
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(test (run "{5 {/ 6 0}}") =error> "non-function")
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(test (run "
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{bind
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{
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{swap!
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{rfun {x y}
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{bind {{tmp x}}
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{set! x y}
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{set! y tmp}
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}
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}
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}
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{a 1}
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{b 2}
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}
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{swap! a b}
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{+ a {* 10 b}}
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}") => 12)
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(test (run "{bind {{make-counter
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{fun {}
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{bind {{c 0}}
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{fun {}
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{set! c {+ 1 c}}
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c}}}}}
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{bind {{c1 {make-counter}}
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{c2 {make-counter}}}
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{* {c1} {c1} {c2} {c1}}}}")
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=> 6)
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(test (run "{bindrec {{foo {fun {}
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{set! foo {fun {} 2}}
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1}}}
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{+ {foo} {* 10 {foo}}}}")
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=> 21)
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(test (run "{bindrec {{fact {fun {n}
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{if {= 0 n}
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1
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{* n {fact {- n 1}}}}}}}
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{fact 5}}")
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=> 120)
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(test (run "
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{bind {{x 10}}
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{bind {{y {set! x 1}}}
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x
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}
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}
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") => 1)
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(test (run "{bind {{x 2}} {set! x 1}}") =error> "run: evaluation returned a bad value: (VoidV)")
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(test (run "{if {= 1 2} 0 1}") => 1)
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(test (run "{if true 1 2}") => 1)
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(test (run "{{fun {x} {+ x 1}} 4}")
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=> 5)
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(test (run "{bind {{add3 {fun {x} {+ x 3}}}} {add3 1}}")
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=> 4)
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(test (run "{bind {{add3 {fun {x} {+ x 3}}}
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{add1 {fun {x} {+ x 1}}}}
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{bind {{x 3}} {add1 {add3 x}}}}")
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=> 7)
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(test (run "{bind {{identity {fun {x} x}}
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{foo {fun {x} {+ x 1}}}}
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{{identity foo} 123}}")
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=> 124)
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(test (run "{bind {{x 3}}
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{bind {{f {fun {y} {+ x y}}}}
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{bind {{x 5}}
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{f 4}}}}")
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=> 7)
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(test (run "{{{fun {x} {x 1}}
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{fun {x} {fun {y} {+ x y}}}}
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123}")
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=> 124)
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;; More tests for complete coverage
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(test (run "{bind x 5 x}") =error> "bad `bind' syntax")
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(test (run "{fun x x}") =error> "parse-sexpr: bad function syntax in (fun x x)")
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(test (run "{if x}") =error> "bad `if' syntax")
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(test (run "{}") =error> "bad syntax")
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(test (run "{bind {{x 5} {x 5}} x}") =error> "parse-sexpr: duplicate `bind' names: (x x)")
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(test (run "{fun {x x} x}") =error> "parse-sexpr: bad parameters defined for function in (fun (x x) x)")
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(test (run "{+ x 1}") =error> "no binding for")
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(test (run "{+ 1 {fun {x} x}}") =error> "bad input")
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(test (run "{+ 1 {fun {x} x}}") =error> "bad input")
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(test (run "{1 2}") =error> "with a non-function")
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(test (run "{{fun {x} x}}") =error> "arity mismatch")
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(test (run "{if {< 4 5} 6 7}") => 6)
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(test (run "{if {< 5 4} 6 7}") => 7)
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(test (run "{if + 6 7}") => 6)
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(test (run "{fun {x} x}") =error> "returned a bad value")
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(test (compile (Num 1)) =error> "compiler is not enabled")
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(test (compile-body (list (Num 1))) =error> "compiler is not enabled")
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(test (compile-get-boxes (list (Id 'x))) =error> "compiler is not enabled")
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(test (run "{bind {{if 5}} if}") =error> "parse-sexpr: bad word found in `bind' : (if)")
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(test (run "{fun {if} if}") =error> "parse-sexpr: bad words found in function parameter names in (fun (if) if)")
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