Re: LPeg for TLV (BER,DER,CER)
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- Subject: Re: LPeg for TLV (BER,DER,CER)
- From: Peter Odding <xolox@...>
- Date: 2008年3月03日 17:41:02 +0100
have run into the issue of how can a Lua Function-based pattern perform captures...
I ran into that as well recently, and the answer seems to be that it
doesn't... You need the explicit match / capture distinction. That is,
when you need to capture something different than the matching substring.
Maybe this would be a nice addition for LPeg 0.8? That is, allow
patterns created with lpeg.P(function() ... end) to return zero or more
captures after the new index? This might seem redundant at first because
lpeg.P(function() ... end) / function() ... end
does the same thing, however any context available in the function that
matches the input has to be recreated in the function that manipulates
the capture(s). Here's the case I ran into, matching Lua long comments
and capturing just the body:
# lpeg.P'--['
* function(input, index)
local i, j = input:find('^%-%-%[(=*)%[.-%]%1%]', index)
return j and j + 1
end
/ function(comment)
local level, body = comment:match('^%-%-%[(=*)%[(.-)%]%1%]$')
return comment, body
end
Assuming my proposal is possible this would become:
# lpeg.P'--['
* function(input, index)
local i, j, body = input:find('^%-%-%[(=*)%[(.-)%]%1%]', index)
if j then return j + 1, body end
end
- Peter Odding
Thomas Harning wrote:
On 2008年2月29日 18:53:41 -0500
Thomas Harning <harningt@gmail.com> wrote:
Does anybody have any suggestions on how to use LPeg 0.6 for TLV
parsing, especially BER?
I've come up with something that mostly works using Lua Function-based
patterns, and have run into the issue of how can a Lua Function-based
pattern perform captures...
The hacky idea I came up w/ is to use something like:
lpeg.C(function) / getFunctionCaptures
Any better ideas?