Re: Lua 5.3.3 empty match behaviour with the '-' modifier
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- Subject: Re: Lua 5.3.3 empty match behaviour with the '-' modifier
- From: Roberto Ierusalimschy <roberto@...>
- Date: 2016年5月12日 10:18:39 -0300
> > Lua 5.3.3 Copyright (C) 1994-2016 Lua.org, PUC-Rio
> > > =(";a;"):gsub("a-", "ITEM")
> > ITEM;ITEMaITEM;ITEM 4
> >
> > I.e. the substring 'a' in ";a;" is not recognized as an instance
> > of the pattern "a-".
>
> The substring 'a' is not an instance of the pattern "a-", given that
> '' is also valid and shorter than 'a'. So, this behavior seems correct.
Complementing my answer: the issue (and the "Python rule") is about
*where* things match, not *how* they match.
The behavior is like that ('|' is the current position):
'|a' x 'a-' -> matches the empty string -> OK.
'|a' x 'a-' -> matches the empty string, but ending at the same position
of previous match -> fail.
'a|' x 'a-' -> goes to next character to try a match.
-- Roberto