Re: [WIP][PATCH 2/2] pkl,pvm: add support for regular expression

[Mohammad-Reza Nabipoor]

Hi Jose.

On Wed, Feb 15, 2023 at 09:38:31PM +0100, Jose E. Marchesi wrote:
> 
> > On Wed, Feb 15, 2023 at 11:01:01AM +0100, Jose E. Marchesi wrote:
> >> 
> >
> >> I don't think it is a good idea to expose the regexp machinery in std
> >> like this.
> >> 
> >> I thought we were targetting adding support for STRING ~ REGEXP at the
> >> language level?  The compiler can then generate calls to _pkl_re_gmatch
> >> and DTRT...
> >> 
> >
> > Yes, I wanted to enable us to use regexp for problems we already have
> > sooner.
> > Because we have to think about the struct patterns as a general mechanism
> > and rushing to implementing regexp at language level can cause problems
> > for us.
> 
> Well, it is difficult to support regexp matching with an operator while
> also supporting matching groups, etc.
> 
> The operator would only evaluate to true or false.  How to convey the
> other information while having ~ return a value that can be used in a
> conditional?
> 
> What we could do is to have both: a ~ operator that returns true/false,
> and also a pk_regexp_gmatch that returns a Pk_Regexp_Match.
> 

What about having a new compile-time type for matched entities.
Both useful in regular expression matching for strings and array of
characters.

Something like this:

```poke
var m1 = "Hello pokers!" ~ /[hH]ello/,
    m2 = [0x00UB, 0x11UB, 0x22UB] ~ /\x11\x22/;

if (m)
  {
    printf "matched at index %v and offset %v\n", m.index_begin, m.offset_begin;
    assert ("Hello pokers!"[m.index_begin:m.index_end] == "Hello");
  }
else
  {
    assert (m.index_begin ?! E_elem);
    assert (m.offset_begin ?! E_elem);
  }
```

We can use other fields for the giving the access to sub-groups.

We can take an approach similar to `Exception` struct.  But for `Matched`.
Compiler can cast it to boolean when necessary.


WDYT?


Regards,
Mohammad-Reza