> On Dec 20, 2016, at 07:54, Alex Knauth <alexan...@knauth.org> wrote:
>
> Oooh, that's pretty cool. Much better than my super-slow attempt.
>
> Should you make this into a package (I would certainly use it a lot)
> or would it make more sense to add in a pull request to the existing
> `match-string` package?
I probably won’t take the time to turn it into a package, if only
because I’m not sure I’d really want that behavior for anything “real”;
I find that most of the time, when using regular expressions, (.*) is
not what you want. In this very example, the code invokes string->number
on one of the captured strings, which implies the pattern your actually
want is:
^(.*)--(\d+) (.*) end$
In reality, my experience is that you often want to use negated
character ranges instead of “.”, so the first capture group would be
([^-]*) instead. At this point, in order to use regular expressions and
have the constraints affect parsing, you need to compile the constraints
into the patterns themselves, not apply them post-hoc. For that reason,
you’d probably effectively want a s-expression regular expression
syntax. Personally, I’d just write this:
[(regexp #px"^([^-]*)--(\\d+) (.*) end$"
(list _ a b c))
...]
If you want to add something like it to your match-string package for
simple cases like this one, though, I won’t have any problem with that,
of course. I’ve just found that, most of the time, once I have something
that gets too complicated to read as an inline regular expression, it’s
easier for me to switch to full-fledged parser combinators rather than
try and prettify regexps.
(Admittedly, though, this has made me realize I should probably enhance
megaparsack to cooperate with match in some way.)
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