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match: check duplicate identifiers across list-no-order patters (#2000)

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* match: check duplicate identifiers across list-no-order patters

* match: document that list-no-order doesn't support duplicate ids between sub-pats

* match: put duplicate id docs in a margin note between the two variants
This commit is contained in:
Alex Knauth 2018-04-11 00:00:14 -04:00 committed by Ben Greenman
parent d0e6a5839f
commit f66b3312df
2 changed files with 52 additions and 18 deletions
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8
pkgs/racket-doc/scribblings/reference/match.scrbl
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@ -155,7 +155,13 @@ In more detail, patterns match as follows:
#:eval match-eval
(match '(1 2 3)
[(list-no-order 3 2 x) x])
]}
]
@margin-note{
Unlike other patterns, @racketidfont{list-no-order} doesn't
allow duplicate identifiers between subpatterns. For example
the patterns @racket[(list-no-order x 1 x)] and
@racket[(list-no-order x 1 x ...)] both produce syntax errors.}}
@item{@racket[(#,(racketidfont "list-no-order") _pat ... _lvp)] ---
generalizes @racketidfont{list-no-order} to allow a pattern

38
racket/collects/racket/match/parse.rkt
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@ -117,9 +117,15 @@
(ddk? #'dd)
(let* ([count (ddk? #'dd)]
[min (if (number? count) count #f)]
[ps (syntax->list #'(p ...))])
(GSeq (cons (list (rearm+parse #'lp))
(for/list ([p ps]) (list (parse p))))
[ps (syntax->list #'(p ...))]
;; parsed versions of ps and lp
[parsed-ps (map parse ps)]
[parsed-lp (rearm+parse #'lp)])
;; duplicates within *one* of the ps is fine, but duplicates
;; *accross multiple* of the ps is an error, at least for now
(check-list-no-order-duplicates (cons parsed-lp parsed-ps))
(GSeq (cons (list parsed-lp)
(for/list ([p parsed-ps]) (list p)))
(cons min (map (lambda _ 1) ps))
(cons #f (map (lambda _ 1) ps))
;; vars in lp are lists, vars elsewhere are not
@ -133,8 +139,13 @@
stx
(ormap (lambda (e) (and (ddk? e) e)) (syntax->list #'(p ...))))]
[(list-no-order p ...)
(let ([ps (syntax->list #'(p ...))])
(GSeq (for/list ([p ps]) (list (rearm+parse p)))
(let* ([ps (syntax->list #'(p ...))]
;; parsed versions of ps
[parsed-ps (map rearm+parse ps)])
;; duplicates within *one* of the ps is fine, but duplicates
;; *accross multiple* of the ps is an error, at least for now
(check-list-no-order-duplicates parsed-ps)
(GSeq (for/list ([p parsed-ps]) (list p))
(map (lambda _ 1) ps)
(map (lambda _ 1) ps)
;; all of these patterns get bound to only one thing
@ -196,4 +207,21 @@
(or (parse-literal (syntax-e #'v))
(raise-syntax-error 'match "syntax error in pattern" disarmed-stx))]))
;; --------------------------------------------------------------
;; check-list-no-order-duplicates : [Listof Pat] -> Void
(define (check-list-no-order-duplicates pats)
;; Duplicate identifiers within *one* pat is fine, but
;; duplicate identifiers across multiple pats is an error.
;; Using the `bound-vars` function on each pat separately
;; should merge duplicate identifiers within each *one*.
;; So, duplicate identifiers in the appended list must be
;; duplicates across multiple.
(define vars (apply append (map bound-vars pats)))
(define dup (check-duplicate-identifier vars))
(when dup
(raise-syntax-error 'list-no-order "unexpected duplicate identifier" dup)))
;; --------------------------------------------------------------
;; (trace parse)