> On Jan 22, 2016, at 9:07 AM, brendan <bren...@cannells.com> wrote:
>
> I was playing around with parser-tools, which has a convenient syntax in
> which the elements of a grammar rule are bound in order to $1, $2, etc. This
> led me to think about how the composability of non-hygienic macros could be
> limited by name-collisions - not very likely in this case, but easier to
> imagine for something like, say, anaphoric if. My understanding of Racket's
> internals is still pretty limited, so I'd like to know if there could be a
> mechanism with which the programmer could specify prefixes for any bindings
> introduced by a particular macro, without requiring explicit support from the
> macro writer?
I was curious, so I tried to write a macro to do that.
I was hoping something like this would work, but it produces
'(prefixed:let-values (((or-part) #f)) (if or-part or-part (or #t)))
Instead of
'(prefixed:let-values (((prefixed:or-part) #f)) (prefixed:if prefixed:or-part
prefixed:or-part (or #t)))
Which is what I was hoping for.
#lang racket/base
(require (for-syntax racket/base
racket/syntax
syntax/parse
(only-in colon-match :match define-:match-class)))
(begin-for-syntax
(define-:match-class stx syntax?)
;; syntax-prefix-introduced-ids : Stx Stx Stx -> Stx
;; Recurs on inner-stx to prefix all the identifiers with the same
;; context as outer-stx.
(define (syntax-prefix-introduced-ids outer-stx prefix inner-stx)
(define (recur inner-stx)
(syntax-prefix-introduced-ids outer-stx prefix inner-stx))
(define e (syntax-e inner-stx))
(:match e
[(? symbol? sym)
(cond [(bound-identifier=? inner-stx (datum->syntax outer-stx sym))
(format-id inner-stx "~a~a" prefix inner-stx
#:source inner-stx #:props inner-stx)]
[else
inner-stx])]
[(list as:stx ...)
(datum->syntax inner-stx (map recur as)
inner-stx inner-stx)]
[(list-rest as:stx ... b:stx)
(datum->syntax inner-stx (append (map recur as) (recur b))
inner-stx inner-stx)]
[_
inner-stx])))
(define-syntax prefix-introduced-ids
(syntax-parser
[(prefix-introduced-ids prefix form)
(define expanded
(local-expand #'form
(syntax-local-context)
#f))
(syntax-prefix-introduced-ids expanded #'prefix expanded)]))
(syntax->datum
(expand-once
#'(prefix-introduced-ids prefixed: (or #false #true))))
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