/usr/share/racket/pkgs/swindle/setf.rkt is in racket-common 6.7-3.
This file is owned by root:root, with mode 0o644.
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;;> This module provides the forms `setf!', `psetf!', and `setf!-values' for
;;> generic setters, much like CL's `setf', and `psetf', and a form similar
;;> to Racket's `set!-values'. Note that when these are later re-exported
;;> (by `turbo'), they are renamed as `set!', `pset!', and `set!-values'
;;> (overriding the built-in `set!' and `set!-values'). Also, note that
;;> this just defines the basic functionality, the `misc' module defines
;;> many common setters.
#lang mzscheme
;;>> (setf! place value ...)
;;> Expand `(setf! (foo ...) v)' to `(set-foo! ... v)'. The generated
;;> `set-foo!' identifier has the same syntax context as `foo', which
;;> means that to use this for some `foo' you need to define `set-foo!'
;;> either as a function or a syntax in the same definition context of
;;> `foo'. The nice feature that comes out of this and the syntax system
;;> is that examples like the following work as expected:
;;> (let ([foo mcar] [set-foo! set-mcar!]) (setf! (foo a) 11))
;;>
;;> `place' gets expanded before this processing is done so macros work
;;> properly. If the place is not a form, then this will just use the
;;> standard `set!'.
;;>
;;> Another extension of the original `set!' is that it allows changing
;;> several places in sequence -- `(setf! x a y b)' will set `x' to `a'
;;> and then set `y' to `b'.
;; Original idea thanks to Eric Kidd who stole it from Dylan
(provide setf!)
(define-syntax (setf! stx)
(define (set!-prefix id)
(datum->syntax-object
id
(string->symbol (string-append "set-" (symbol->string (syntax-e id)) "!"))
id id))
(syntax-case stx (setf!)
;; if the getter is a set!-transformer, make it do its thing
[(setf! getter . xs)
(and (identifier? #'getter)
(set!-transformer? (syntax-local-value #'getter (lambda () #f))))
((set!-transformer-procedure (syntax-local-value #'getter)) stx)]
[(setf! place val)
;; need to expand place first, in case it is itself a macro
(with-syntax ([place (local-expand
#'place 'expression
(append (list #'#%app #'#%top #'#%datum)
(map (lambda (s)
(datum->syntax-object #'place s #f))
'(#%app #%top #%datum))))])
(syntax-case #'place ()
[(getter args ...)
(if (identifier? #'getter)
(with-syntax ([setter (set!-prefix #'getter)])
(syntax/loc stx (setter args ... val)))
(raise-syntax-error #f "not an identifier" stx #'getter))]
[_ (syntax/loc stx (set! place val))]))]
[(setf! place val . more)
(let loop ([pvs #'(place val . more)] [r '()])
(syntax-case pvs ()
[(p v . more)
(loop #'more (cons (syntax/loc stx (setf! p v)) r))]
[() (quasisyntax/loc stx (begin #,@(reverse r)))]
[_ (raise-syntax-error #f "uneven number of forms" stx)]))]))
;;>> (psetf! place value ...)
;;> This is very similar to `setf!' above, except that the change to the
;;> places is done *simultaneously*. For example, `(setf! x y y x)'
;;> switches the values of the two variables.
;; This could have been expressed using `setf!-values', but that would lead to
;; an unnecessary creation of a values tuple.
(provide psetf!)
(define-syntax (psetf! stx)
(syntax-case stx ()
;; optimize common case
[(_ place val) (syntax/loc stx (setf! place val))]
[(_ more ...)
(let loop ([vars '()] [vals '()] [more (syntax->list #'(more ...))])
(cond
[(null? more)
(let ([vars (reverse vars)]
[vals (reverse vals)]
[tmps (generate-temporaries (map (lambda (x) 'x) vars))])
(quasisyntax/loc stx
(let #,(map (lambda (t v) #`(#,t #,v)) tmps vals)
#,@(map (lambda (v t) #`(setf! #,v #,t)) vars tmps))))]
[(null? (cdr more))
(raise-syntax-error #f "uneven number of forms" stx)]
[else (loop (cons (car more) vars) (cons (cadr more) vals)
(cddr more))]))]))
;;>> (setf!-values (place ...) expr)
;;> This is a version of `setf!', that works with multiple values. `expr'
;;> is expected to evaluate to the correct number of values, and these are
;;> then put into the specified places which can be an place suited to
;;> `setf!'. Note that no duplication of identifiers is checked, if an
;;> identifier appears more than once then it will have the last assigned
;;> value.
(provide setf!-values)
(define-syntax (setf!-values stx)
(syntax-case stx ()
;; optimize common case
[(_ (place) val) (syntax/loc stx (setf! place val))]
[(_ (place ...) values)
(with-syntax ([(temp ...) (datum->syntax-object
#'(place ...)
(generate-temporaries #'(place ...))
#'(place ...))])
(syntax/loc stx
(let-values ([(temp ...) values])
(setf! place temp) ...)))]))
;;>> (set-values! places ... values-expr)
;;>> (set-list! places ... list-expr)
;;>> (set-vector! places ... vector-expr)
;;> These are defined as special forms that use `setf!-values' to set the
;;> given places to the appropriate components of the third form. This
;;> allows foing the following:
;;> => (define (values a b c) (values 1 2 3))
;;> => (setf! (values a b c) (values 11 22 33))
;;> => (list a b c)
;;> (11 22 33)
;;> => (setf! (list a b c) (list 111 222 333))
;;> => (list a b c)
;;> (111 222 333)
;;> => (setf! (list a b c) (list 1111 2222 3333))
;;> => (list a b c)
;;> (1111 2222 3333)
;;> Furthermore, since the individual setting of each place is eventually
;;> done with `setf!', then this can be used recursively:
;;> => (set! (list a (vector b) (vector c c)) '(2 #(3) #(4 5)))
;;> => (list a b c)
;;> (2 3 5)
(provide set-values! set-list! set-vector!)
(define-syntaxes (set-values! set-list! set-vector!)
(let ([make-setter
(lambda (convert)
(lambda (stx)
(syntax-case stx ()
[(_ x y ...)
(let loop ([args (syntax->list #'(x y ...))] [as '()])
(if (null? (cdr args))
(quasisyntax/loc stx
(setf!-values #,(datum->syntax-object
#'(x y ...) (reverse as) #'(x y ...))
#,(convert (car args))))
(loop (cdr args) (cons (car args) as))))])))])
(values
;; set-values!
(make-setter (lambda (x) x))
;; set-list!
(make-setter (lambda (x) #`(apply values #,x)))
;; set-vector!
(make-setter (lambda (x) #`(apply values (vector->list #,x)))))))
(provide shift! rotate! inc! dec! push! pop!)
(define-syntaxes (shift! rotate! inc! dec! push! pop!)
(let* ([protect-indexes
(lambda (place body)
(syntax-case place ()
[(getter . xs)
(let ([bindings+expr
(let loop ([xs #'xs]
[bindings '()]
[expr (list #'getter)]
[all-ids? #t])
(syntax-case xs ()
[() (and (not all-ids?)
(cons (reverse bindings) (reverse expr)))]
[(x . xs)
(let ([new (datum->syntax-object
#'x (gensym) #'x)])
(loop #'xs
(cons (list new #'x) bindings)
(cons new expr)
(and (identifier? #'x) all-ids?)))]
[x (and (not (and all-ids? (identifier? #'x)))
(let ([new (datum->syntax-object
#'x (gensym) #'x)])
(cons (reverse (cons (list new #'x)
bindings))
(append (reverse expr) new))))]))])
(if bindings+expr
#`(let #,(car bindings+expr) #,(body (cdr bindings+expr)))
(body place)))]
[_ (body place)]))]
[protect-indexes-list
(lambda (places body)
(let loop ([ps places] [r '()])
(if (null? ps)
(body (reverse r))
(protect-indexes (car ps) (lambda (p)
(loop (cdr ps) (cons p r)))))))])
(values
;;>> (shift! place ... newvalue)
;;> This is similar to CL's `shiftf' -- it is roughly equivalent to
;;> (begin0 place1
;;> (psetf! place1 place2
;;> place2 place3
;;> ...
;;> placen newvalue))
;;> except that it avoids evaluating index subforms twice, for example:
;;> => (let ([foo (lambda (x) (printf ">>> ~s\n" x) x)]
;;> [a '(1)] [b '(2)])
;;> (list (shift! (car (foo a)) (car (foo b)) 3) a b))
;;> >>> (1)
;;> >>> (2)
;;> (1 (2) (3))
;; --- shift!
(lambda (stx)
(syntax-case stx ()
[(_ x y more ...)
(protect-indexes-list (syntax->list #'(x y more ...))
(lambda (vars)
(let loop ([vs vars] [r '()])
(if (null? (cdr vs))
(quasisyntax/loc stx
(let ([v #,(car vars)])
(psetf! #,@(datum->syntax-object
#'(x y more ...)
(reverse r)
#'(x y more ...)))
v))
(loop (cdr vs) (list* (cadr vs) (car vs) r))))))]))
;;>> (rotate! place ...)
;;> This is similar to CL's `rotatef' -- it is roughly equivalent to
;;> (psetf! place1 place2
;;> place2 place3
;;> ...
;;> placen place1)
;;> except that it avoids evaluating index subforms twice.
;; --- rotate!
(lambda (stx)
(syntax-case stx ()
[(_ x) #'(void)]
[(_ x xs ...)
(protect-indexes-list (syntax->list #'(x xs ...))
(lambda (vars)
(let loop ([vs vars] [r '()])
(if (null? (cdr vs))
(quasisyntax/loc stx
(psetf! #,@(datum->syntax-object
#'(x xs ...)
(reverse (list* (car vars) (car vs) r))
#'(x xs ...))))
(loop (cdr vs) (list* (cadr vs) (car vs) r))))))]))
;;>> (inc! place [delta])
;;>> (dec! place [delta])
;;>> (push! x place)
;;>> (pop! place)
;;> These are some simple usages of `setf!'. Note that they also avoid
;;> evaluating any indexes twice.
;; --- inc!
(lambda (stx)
(syntax-case stx ()
[(_ p) #'(_ p 1)]
[(_ p d) (protect-indexes #'p
(lambda (p) #`(setf! #,p (+ #,p d))))]))
;; --- dec!
(lambda (stx)
(syntax-case stx ()
[(_ p) #'(_ p 1)]
[(_ p d) (protect-indexes #'p
(lambda (p) #`(setf! #,p (- #,p d))))]))
;; --- push!
(lambda (stx)
(syntax-case stx ()
[(_ x p) (protect-indexes #'p
(lambda (p) #`(setf! #,p (cons x #,p))))]))
;; --- pop!
(lambda (stx)
(syntax-case stx ()
[(_ p) (protect-indexes #'p
(lambda (p)
#`(let ([p1 #,p])
(begin0 (car p1) (setf! #,p (cdr p1))))))])))))
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