unhandled exception: index -1 not in 0 .. 12 [IndexDefect]

[Isofruit]

Even _if_ syntax sugar were available I would recommend the more verbose 
approach, simply for clarity.
    
    
    let matchCount = customregex() # return number of matches
    let hasMatches = matchCount > 0
    if hasMatches:
      for i in 0 .. matchCount:
    
    
    Run

This would honestly be more elegant though if `customregex` didn't return the 
number of matches, but the matches themselves. What you actually want to 
express is to do X _per match_ , right? So imo what you actually seem to want 
is a `for _ in matches:` loop.