229 lines
8.4 KiB
Racket
229 lines
8.4 KiB
Racket
; Reference implementation of SRFI-71 using PLT 208's modules
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; Sebastian.Egner@philips.com, 29-Apr-2005
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#lang scheme/base
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(provide srfi-let
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srfi-let*
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srfi-letrec
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srfi-letrec*
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uncons unlist unvector
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values->list values->vector
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uncons-2 uncons-3 uncons-4
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uncons-cons)
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; --- textual copy of 'letvalues.scm' starts here ---
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; Reference implementation of SRFI-71 (generic part)
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; Sebastian.Egner@philips.com, 20-May-2005, PLT 208
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;
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; In order to avoid conflicts with the existing let etc.
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; the macros defined here are called srfi-let etc.,
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; and they are defined in terms of r5rs-let etc.
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; It is up to the actual implementation to save let/*/rec
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; in r5rs-let/*/rec first and redefine let/*/rec
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; by srfi-let/*/rec then.
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;
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; There is also a srfi-letrec* being defined (in view of R6RS.)
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;
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; Macros used internally are named i:<something>.
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;
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; Abbreviations for macro arguments:
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; bs - <binding spec>
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; b - component of a binding spec (values, <variable>, or <expression>)
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; v - <variable>
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; vr - <variable> for rest list
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; x - <expression>
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; t - newly introduced temporary variable
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; vx - (<variable> <expression>)
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; rec - flag if letrec is produced (and not let)
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; cwv - call-with-value skeleton of the form (x formals)
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; (call-with-values (lambda () x) (lambda formals /payload/))
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; where /payload/ is of the form (let (vx ...) body1 body ...).
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;
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; Remark (*):
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; We bind the variables of a letrec to i:undefined since there is
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; no portable (R5RS) way of binding a variable to a values that
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; raises an error when read uninitialized.
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(define i:undefined 'undefined)
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(define-syntax srfi-letrec* ; -> srfi-letrec
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(syntax-rules ()
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((srfi-letrec* () body1 body ...)
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(srfi-letrec () body1 body ...))
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((srfi-letrec* (bs) body1 body ...)
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(srfi-letrec (bs) body1 body ...))
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((srfi-letrec* (bs1 bs2 bs ...) body1 body ...)
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(srfi-letrec (bs1) (srfi-letrec* (bs2 bs ...) body1 body ...)))))
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(define-syntax srfi-letrec ; -> i:let
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(syntax-rules ()
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((srfi-letrec ((b1 b2 b ...) ...) body1 body ...)
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(i:let "bs" #t () () (body1 body ...) ((b1 b2 b ...) ...)))))
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(define-syntax srfi-let* ; -> srfi-let
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(syntax-rules ()
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((srfi-let* () body1 body ...)
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(srfi-let () body1 body ...))
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((srfi-let* (bs) body1 body ...)
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(srfi-let (bs) body1 body ...))
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((srfi-let* (bs1 bs2 bs ...) body1 body ...)
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(srfi-let (bs1) (srfi-let* (bs2 bs ...) body1 body ...)))))
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(define-syntax srfi-let ; -> i:let or i:named-let
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(syntax-rules ()
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((srfi-let ((b1 b2 b ...) ...) body1 body ...)
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(i:let "bs" #f () () (body1 body ...) ((b1 b2 b ...) ...)))
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((srfi-let tag ((b1 b2 b ...) ...) body1 body ...)
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(i:named-let tag () (body1 body ...) ((b1 b2 b ...) ...)))))
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(define-syntax i:let
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(syntax-rules (values)
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; (i:let "bs" rec (cwv ...) (vx ...) body (bs ...))
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; processes the binding specs bs ... by adding call-with-values
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; skeletons to cwv ... and bindings to vx ..., and afterwards
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; wrapping the skeletons around the payload (let (vx ...) . body).
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; no more bs to process -> wrap call-with-values skeletons
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((i:let "bs" rec (cwv ...) vxs body ())
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(i:let "wrap" rec vxs body cwv ...))
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; recognize form1 without variable -> dummy binding for side-effects
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((i:let "bs" rec cwvs (vx ...) body (((values) x) bs ...))
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(i:let "bs" rec cwvs (vx ... (dummy (begin x #f))) body (bs ...)))
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; recognize form1 with single variable -> just extend vx ...
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((i:let "bs" rec cwvs (vx ...) body (((values v) x) bs ...))
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(i:let "bs" rec cwvs (vx ... (v x)) body (bs ...)))
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; recognize form1 without rest arg -> generate cwv
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((i:let "bs" rec cwvs vxs body (((values v ...) x) bs ...))
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(i:let "form1" rec cwvs vxs body (bs ...) (x ()) (values v ...)))
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; recognize form1 with rest arg -> generate cwv
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((i:let "bs" rec cwvs vxs body (((values . vs) x) bs ...))
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(i:let "form1+" rec cwvs vxs body (bs ...) (x ()) (values . vs)))
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; recognize form2 with single variable -> just extend vx ...
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((i:let "bs" rec cwvs (vx ...) body ((v x) bs ...))
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(i:let "bs" rec cwvs (vx ... (v x)) body (bs ...)))
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; recognize form2 with >=2 variables -> transform to form1
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((i:let "bs" rec cwvs vxs body ((b1 b2 b3 b ...) bs ...))
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(i:let "form2" rec cwvs vxs body (bs ...) (b1 b2) (b3 b ...)))
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; (i:let "form1" rec cwvs vxs body bss (x (t ...)) (values v1 v2 v ...))
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; processes the variables in v1 v2 v ... adding them to (t ...)
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; and producing a cwv when finished. There is not rest argument.
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((i:let "form1" rec (cwv ...) vxs body bss (x ts) (values))
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(i:let "bs" rec (cwv ... (x ts)) vxs body bss))
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((i:let "form1" rec cwvs (vx ...) body bss (x (t ...)) (values v1 v ...))
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(i:let "form1" rec cwvs (vx ... (v1 t1)) body bss (x (t ... t1)) (values v ...)))
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; (i:let "form1+" rec cwvs vxs body bss (x (t ...)) (values v ... . vr))
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; processes the variables in v ... . vr adding them to (t ...)
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; and producing a cwv when finished. The rest arg is vr.
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((i:let "form1+" rec cwvs (vx ...) body bss (x (t ...)) (values v1 v2 . vs))
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(i:let "form1+" rec cwvs (vx ... (v1 t1)) body bss (x (t ... t1)) (values v2 . vs)))
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((i:let "form1+" rec (cwv ...) (vx ...) body bss (x (t ...)) (values v1 . vr))
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(i:let "bs" rec (cwv ... (x (t ... t1 . tr))) (vx ... (v1 t1) (vr tr)) body bss))
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((i:let "form1+" rec (cwv ...) (vx ...) body bss (x ()) (values . vr))
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(i:let "bs" rec (cwv ... (x tr)) (vx ... (vr tr)) body bss))
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; (i:let "form2" rec cwvs vxs body bss (v ...) (b ... x))
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; processes the binding items (b ... x) from form2 as in
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; (v ... b ... x) into ((values v ... b ...) x), i.e. form1.
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; Then call "bs" recursively.
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((i:let "form2" rec cwvs vxs body (bs ...) (v ...) (x))
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(i:let "bs" rec cwvs vxs body (((values v ...) x) bs ...)))
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((i:let "form2" rec cwvs vxs body bss (v ...) (b1 b2 b ...))
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(i:let "form2" rec cwvs vxs body bss (v ... b1) (b2 b ...)))
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; (i:let "wrap" rec ((v x) ...) (body ...) cwv ...)
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; wraps cwv ... around the payload generating the actual code.
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; For letrec this is of course different than for let.
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((i:let "wrap" #f vxs body)
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(let vxs . body))
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((i:let "wrap" #f vxs body (x formals) cwv ...)
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(call-with-values
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(lambda () x)
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(lambda formals (i:let "wrap" #f vxs body cwv ...))))
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((i:let "wrap" #t vxs body)
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(letrec vxs . body))
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((i:let "wrap" #t ((v t) ...) body cwv ...)
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(let ((v i:undefined) ...) ; (*)
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(i:let "wraprec" ((v t) ...) body cwv ...)))
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; (i:let "wraprec" ((v t) ...) body cwv ...)
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; generate the inner code for a letrec. The variables v ...
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; are the user-visible variables (bound outside), and t ...
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; are the temporary variables bound by the cwv consumers.
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((i:let "wraprec" ((v t) ...) (body ...))
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(begin (set! v t) ... (let () body ...)))
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((i:let "wraprec" vxs body (x formals) cwv ...)
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(call-with-values
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(lambda () x)
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(lambda formals (i:let "wraprec" vxs body cwv ...))))
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))
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(define-syntax i:named-let
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(syntax-rules (values)
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; (i:named-let tag (vx ...) body (bs ...))
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; processes the binding specs bs ... by extracting the variable
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; and expression, adding them to vx and turning the result into
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; an ordinary named let.
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((i:named-let tag vxs body ())
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(let tag vxs . body))
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((i:named-let tag (vx ...) body (((values v) x) bs ...))
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(i:named-let tag (vx ... (v x)) body (bs ...)))
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((i:named-let tag (vx ...) body ((v x) bs ...))
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(i:named-let tag (vx ... (v x)) body (bs ...)))))
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; --- standard procedures ---
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(define (uncons pair)
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(values (car pair) (cdr pair)))
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(define (uncons-2 list)
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(values (car list) (cadr list) (cddr list)))
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(define (uncons-3 list)
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(values (car list) (cadr list) (caddr list) (cdddr list)))
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(define (uncons-4 list)
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(values (car list) (cadr list) (caddr list) (cadddr list) (cddddr list)))
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(define (uncons-cons alist)
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(values (caar alist) (cdar alist) (cdr alist)))
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(define (unlist list)
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(apply values list))
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(define (unvector vector)
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(apply values (vector->list vector)))
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; --- standard macros ---
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(define-syntax values->list
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(syntax-rules ()
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((values->list x)
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(call-with-values (lambda () x) list))))
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(define-syntax values->vector
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(syntax-rules ()
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((values->vector x)
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(call-with-values (lambda () x) vector))))
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; --- textual copy of 'letvalues.scm' ends here ---
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