Re: [Bug-apl] Regex support

[Giuseppe Cocomazzi]

Hi,
I also think that adding the support would be very useful. However, I
would definitely avoid PCRE and backreference support. I think the
best solution would be to just add a basic and efficient NFA-based
implementation (the defacto original implementation for Unix). For
more information about the correct way to implement RE:
https://swtch.com/~rsc/regexp/

As for the API itself, I agree with Elias that maybe a simple
interface is the way to go. I would also prefer not to have any
support for modifiers (not even IGNORECASE) and definitely avoid the
MULTILINE horror. If we opt for the NFA implementation then, the
builtin ⎕Regex (or ⎕RE) could be universally used not only for strings
but for numeric data as well. That, in conjuction with APL arrays,
would ultimately be a killer feature (I am not aware of such a feature
in other languages).

Best,

Giuseppe Cocomazzi
http://sbudella.altervista.org


On Wed, Sep 20, 2017 at 5:59 AM, Elias Mårtenson <address@hidden> wrote:
> On several occasions, I have felt that built-in regex support in GNU APL
> would be very helpful.
>
> Implementing it should be rather simple, but I'd like to discuss how such an
> API should look in order for it to be as useful as possible.
>
> I was thinking of the following form:
>
>       regex ⎕Regex string
>
> The way I envision this to work, is to have the function return ⍬ if there
> is no match, or a string containing the match, if there is one:
>
>       'f..' ⎕Regex 'xzooy'
> ┏⊖┓
> ┃0┃
> ┗━┛
>       'f..' ⎕Regex 'xfooy'
> 'foo'
>
> If the regex has subexpressions, those matches should be returned as
> individual strings:
>
>       '([0-9]+)-([0-9]+)-([0-9]+) '⎕Regex '2017-01-02'
> ┏→━━━━━━━━━━━━━━━┓
> ┃"2017" "01" "02"┃
> ┗∊━━━━━━━━━━━━━━━┛
>
> This would be a very useful API, and reasonably easy to implement by simply
> calling into the standard regcomp() call:
> http://pubs.opengroup.org/onlinepubs/009695399/functions/regcomp.html
>
> What do you think? Is this a reasonable way to implement it? Any suggestions
> about alternative API's?
>
> Regards,
> Elias