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Traverse syntax eagerly in syntax-search-everything #843

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20 changes: 19 additions & 1 deletion private/syntax-traversal.rkt
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Original file line number Diff line number Diff line change
Expand Up @@ -89,8 +89,26 @@
[_ (stream)])))))


;; Returns stx and every syntax object nested within it, in depth-first preorder. This traversal is
;; eager, even though it's exposed as a stream, because building it lazily costs far more than the
;; list it saves allocating: every caller consumes nearly all of the traversal anyway, and this runs
;; on every syntax object the expander visits.
(define (syntax-search-everything stx)
(stream-cons stx (syntax-search stx #:skip-root? #true [_ (syntax-search-everything this-syntax)])))
(define subforms-in-reverse '())
(let loop ([stx stx])
(set! subforms-in-reverse (cons stx subforms-in-reverse))
(syntax-parse stx
[(part ...)
#:cut
(for ([part-stx (in-list (attribute part))])
(loop part-stx))]
[(part ...+ . tail-part)
#:cut
(for ([part-stx (in-list (attribute part))])
(loop part-stx))
(loop #'tail-part)]
[_ (void)]))
(reverse subforms-in-reverse))


(module+ test
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