Re: some newbie questions about lpeg
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- Subject: Re: some newbie questions about lpeg
- From: roberto@... (Roberto Ierusalimschy)
- Date: 2007年9月17日 13:08:08 -0300
> On 9/16/07, gary ng <garyng2000@yahoo.com> wrote:
> > What would be the equivalent of pattern{x,y} in regex,
> > i.e. pattern can occur between x and y times ?
>
> First attempt:
>
> function lpeg.minmax(patt,min,max)
> return #(lpeg.P(patt)^min) * lpeg.P(patt)^-max
> end
Second attempt: (It is much more work, but the result is more efficient,
as it does not read the patterns twice.)
local function mult (p, n)
local np = m.P(true)
while n >= 1 do
if n%2 >= 1 then np = np * p end
p = p * p
n = n/2
end
return np
end
local function minmax (p, min, max)
if max == true then return p^min
else
max = (max == false) and min or max
if max < min then return m.P(false) end
local r = mult(p, min)
if max > min then r = r * p^(min - max) end
return r
end
end
(max == true means no maximum; max == false means exactly min repetitions)
(The next version of 're' will support this syntax.)
-- Roberto