Re: regex-split for Guile

[William James <w_a_x_man@yahoo.com>]

Neil Jerram wrote:

> Thanks for posting that!  For fun/interest, here's an alternative
> implementation that occurred to me.
> 
>        Neil

Thanks for the feedback.

> 
> 
> (use-modules (ice-9 regex)
>              (ice-9 string-fun))
> 
> (define (regex-split regex str . opts)
>   (let* ((unique-char #\@)
>          (unique-char-string (string unique-char)))
>     (let ((splits (separate-fields-discarding-char
>                    unique-char
>                    (regexp-substitute/global #f
>                                              regex
>                                              str
>                                              'pre
>                                              unique-char-string
>                                              0
>                                              unique-char-string
>                                              'post)
>                    list)))

This is an approach that I used some years ago in Awk.
ASCII code 1 is used as the unique character:

# Produces array of nonmatching and matching
# substrings. The size of the array will
# always be an odd number. The first and the
# last item will always be nonmatching.
function shatter( s, shards, regexp )
{ gsub( regexp, "\1&\1", s  )
  return split( s, shards, "\1" )
}


>       (cond ((memq 'keep opts)
>              splits)
>             (else
>              (let ((non-matches (map (lambda (i)
>                                        (list-ref splits (* i 2)))
>                                      (iota (floor (/ (1+ (length 
> splits)) 
> 2))))))
>                (if (memq 'trim opts)
>                    (filter (lambda (s)
>                              (not (zero? (string-length s))))
>                            non-matches)
>                    non-matches)))))))

The way that I want 'trim to work is to remove just the
leading and trailing empty strings.  In Ruby, trailing
null strings are removed by default:

",foo,,,bar,".split( "," )
    ==>["", "foo", "", "", "bar"]