Re: Prefixes of Lpeg patterns

[Roberto Ierusalimschy <roberto@...>]

> Oh, sorry! Should be:
> 
> if for all strings s either B fails on s or A does not fail and
>     B:match(s) <= A:match(s)
> 
> As stated this is not computable, of course. But in certain cases
> it may be logically equivalent to a computable statement. So
> if s and t are strings lpeg.P(s) <= lpeg.P(t) if and only if
> s is a prefix of t.

I don't think that is true. match("a", "a") returns 2, but match("ab",
"a") fails; so, by your definition, match("a", "a") </= match("ab", "a").
(and, so, lpeg.P("a") </= lpeg.P("ab")). ('</=' stands for 'not <='...)

-- Roberto