> On Feb 2, 2018, at 3:21 PM, Matthew Butterick <m...@mbtype.com> wrote:
>> On Feb 2, 2018, at 10:23 AM, 'John Clements' via Racket Users
>> <firstname.lastname@example.org> wrote:
>> This macro gets the names in much closer to the corresponding patterns than
>> matching by index, but it doesn’t actually embed the names into the regexp.
> If you like keeping the names and patterns together, you could also create an
> association list of the names and subpatterns, and iterate:
> #lang racket
> (define msg "2018-02-02T11:26:34 someuser some-computername01 184.108.40.206
> something broke")
> (with-input-from-string msg
> (for/hash ([(name pat) (in-dict '((date . "[-\\dT:]+")
> (username . "\\w+")
> (hostname . "[-\\w\\d]+")
> (ip . "[\\d\\.]+")
> (message . ".+")))])
> (values name (car (regexp-match (pregexp pat)
Oh, that’s nice.
In fact, I’ll tell you what I *really* like about that; it could radically
simplify the irritating process of debugging regexps by breaking them in
various places to perform a binary search; you could instead provide a nice
error message specifying exactly which part of the regexp failed to match.
One thing to be aware of is that you’d need to make sure that your regexp still
works without backtracking. If you broke #px”.*abc” into #px”.*” and #px”abc”,
it wouldn’t mean the same thing any more.
> '#hash((message . #" something broke")
> (date . #"2018-02-02T11:26:34")
> (username . #"someuser")
> (hostname . #"some-computername01")
> (ip . #"220.127.116.11"))
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