Re: how to translate lua pattern "(.*)and(.*)" with lpeg re ?
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- Subject: Re: how to translate lua pattern "(.*)and(.*)" with lpeg re ?
- From: albertmcchan <albertmcchan@...>
- Date: 2018年1月20日 19:54:42 -0500
On Jan 20, 2018, at 5:54 PM, Sean Conner <sean@conman.org> wrote:
> It was thus said that the Great albertmcchan once stated:
>> local C, P = lpeg.C, lpeg.P
>>
>> -- my attempt for lua pettern "(.+)and(.*)"
>> local lpeg_pat = C((P(1) - 'and')^1) * 'and' * C(P(1)^0)
>> local re_pat = re.compile "{ (. ! 'and')* . } 'and' {.*}"
>>
>> -- lua pattern "(.*)and(.*)
>> lpeg_pat = C((P(1) - 'and')^0) 'and' * C(P(1)^0)
>>
>> -- what is lpeg re equivalent code ?
>
> That was weird. I would expect
>
> C((P(1) - 'and')^1) * 'and' * C(P(1)^0)
>
> to map to:
>
> { ( . ! 'and' )+ } 'and' { .* }
>
> but it didn't. I went so far as to recompile LPeg with debugging so I could
> dump the parse tree. The LPeg that works dumped out:
>
> []
> seq
> seq
> capture kind: 'simple' key: 0
> seq
> seq
> not
> seq
> char 'a'
> seq
> char 'n'
> char 'd'
> any
> rep
> seq
> not
> seq
> char 'a'
> seq
> char 'n'
> char 'd'
> any
> seq
> char 'a'
> seq
> char 'n'
> char 'd'
> capture kind: 'simple' key: 0
> rep
> any
>
> While the re code dumped out as:
>
> []
> seq
> seq
> capture kind: 'simple' key: 0
> seq
> seq
> any -- !!!!!!
> not
> seq
> char 'a'
> seq
> char 'n'
> char 'd'
> rep
> seq
> any
> not
> seq
> char 'a'
> seq
> char 'n'
> char 'd'
> seq
> char 'a'
> seq
> char 'n'
> char 'd'
> capture kind: 'simple' key: 0
> rep
> any
>
> The difference is marked. I then tried:
>
> { (! 'and' . )+ } 'and' {.*}
>
> (NOTE: I swapped the order in the first bit) and that produced the same
> code as the LPeg version. So to answer your question, the re equivalent
> code would be:
>
> { (! 'and' .)* } 'and' {.*}
>
> -spc
>