• Subject: Re: Lua to LPEG?
• From: Xavier Wang <weasley.wx@...>
• Date: Tue, 21 Jun 2011 20:22:12 +0800

2011/6/21 Daurnimator
On 21 June 2011 17:37, Dirk Laurie <dpl@sun.ac.za> wrote:
> I am tempted to ask (but won't) why there isn't any lpeg.L(lpat) that
> returns an lpeg pattern that matches the same strings, and returns
> the same captures, that the Lua pattern lpat would.
>
> Instead, I'm asking whether a question similar to this has burgeoned
> in the brain of a list member for long enough that some work in this
> direction has been done.
>
> Dirk
>
>

I started working on it after I saw this post:
local lpeg = require "lpeg"
local P , R , S , V = lpeg.P , lpeg.R , lpeg.S , lpeg.V
local C , Carg , Cb , Cc , Cf , Cg , Ct , Cmt = lpeg.C , lpeg.Carg ,
lpeg.Cb , lpeg.Cc , lpeg.Cf , lpeg.Cg , lpeg.Ct , lpeg.Cmt
local locale = lpeg.locale ( )

local patt_or = function ( patt1 , patt2 )
return patt1 + patt2
end
local patt_then = function ( patt1 , patt2 )
return patt1 * patt2
end

local makerange = function ( from , to )
return R(from .. to)
end

local classes = setmetatable ( {
a = locale.alpha ;
c = locale.cntrl ;
d = locale.digit ;
l = locale.lower ;
p = locale.punct ;
s = locale.space ;
u = locale.upper ;
w = locale.alnum ;
x = locale.xdigit ;
z = P("\0") ;
} , { __index = function(conv,k)
error("Invalid class: " .. k)
return P(k)
end
} )

local any = P(1)
local eos = P(-1)

local luapattern = P{
"pattern";
special = S"^\$()%.[]*+-?" ;
plain = 1-V"special" ;
range = C(V"plain") * "-" * C(V"plain") / makerange ;
class = P"."*Cc(any) + P"%"*(locale.alnum/classes+(1-locale.alnum/P))
+ V"plain"/P ;
set = Cf(P"[" * (P"^"*Cc("complement"))^-1 * (V"range" + V"class")^1
* P"]" , patt_or) ;
item = V"set" + V"plain"^1 ;
pattern = Cf( ((-V"item")*any)^-1 * V"item"^0 * (P"\$"*Cc(eos))^-1 ,
patt_then );
}
f = luapattern:match("[%a][%d]")
--lpeg.print(f)
print((f):match("dd6"))

I'm interesting with lpeg now :)

A question: How to match the patten between m to n times?
there is something like patt{m,n}?
I have tried patt^m^-n but it just act like patt^0 :(