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bug#27659: 26.0.50; Add string-matched-text: string-match + match-string
From: |
Stefan Monnier |
Subject: |
bug#27659: 26.0.50; Add string-matched-text: string-match + match-string |
Date: |
Fri, 21 Jul 2017 09:34:44 -0400 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux) |
>> This looks useful, but I think it would be even better to add it
>> as a pcase macro to be composable (see attached patch).
Hey, very nice. Please add it to rx.el.
[ But please change `backref-var` to just `backref` (you can distinguish
the two based on the type of the argument, I think). I guess one
could also argue that you could similarly rename the `let` to
`group-n`. ]
> Although, i must admit i am not fluent in `rx' syntaxis, i find your idea
> very nice.
If you prefer the standard/cryptic regexp syntax, I posted a similar
thingy in the past (see below).
This lets you do
(pcase "foo-123"
((re-match "[[:alpha:]]+-\\(?num:[0-9]+\\)")
num))
=> "123"
Maybe I should install it in pcase.el?
Stefan
(pcase-defmacro re-match (re)
"Matches a string if that string matches RE.
RE should be a regular expression (a string).
It can use the special syntax \\(?VAR: to bind a sub-match
to variable VAR. All other subgroups are treated as shy.
Multiple uses of this macro in a single `pcase' are not optimized
together, so don't expect lex-like performance. But in order for
such optimization to be possible in some distant future, back-references
are not supported."
(let ((start 0)
(last 0)
(new-re '())
(vars '())
(gn 0))
(while (string-match "\\\\(\\(?:\\?\\([-[:alnum:]]*\\):\\)?" re start)
(setq start (match-end 0))
(let ((beg (match-beginning 0))
(name (match-string 1 re)))
;; Skip false positives, either backslash-escaped or within [...].
(when (subregexp-context-p re start last)
(cond
((null name)
(push (concat (substring re last beg) "\\(?:") new-re))
((string-match "\\`[0-9]" name)
(error "Variable can't start with a digit: %S" name))
(t
(let* ((var (intern name))
(id (cdr (assq var vars))))
(unless id
(setq gn (1+ gn))
(setq id gn)
(push (cons var gn) vars))
(push (concat (substring re last beg) (format "\\(?%d:" id))
new-re))))
(setq last start))))
(push (substring re last) new-re)
(setq new-re (mapconcat #'identity (nreverse new-re) ""))
`(and (pred stringp)
(app (lambda (s)
(save-match-data
(when (string-match ,new-re s)
(vector ,@(mapcar (lambda (x) `(match-string ,(cdr x) s))
vars)))))
(,'\` [,@(mapcar (lambda (x) (list '\, (car x))) vars)])))))
bug#27659: 26.0.50; Add string-matched-text: string-match + match-string, Michael Heerdegen, 2017/07/21