Re: [NTG-context] lpeg substitution

11 Aug 2009


      Thomas A. Schmitz wrote:
...
Hi all,
I'm working on my Greek module again and am trying to filter and massage 
the input via lpeg, but there's something I don't quite get. As a 
minimal example: suppose I want to substitute A and B in my input with X 
and leave all other letters alone. Here's my attempt:
brrr ... massaging input ... can be dangerous ... anyhow, here you go

\startluacode
     local replace = {
         A = "X",
         B = "X",
     }
     setmetatable(replace, { __index = function(t,k)
         return k
     end })

     local dosub = (lpeg.Cs(1)) / replace

     local subs =
         (dosub)^0

     function test (string)
     tex.sprint(lpeg.match(subs,string))
     end

\stopluacode

\def\Substitute#1{\ctxlua{test("#1")}}

\starttext

\Substitute{thomas ABC whatever}

\stoptext

and yes, it's slow; the next variant is faster but takes a bit more 
memory (neglectable compared to what is alrwady taken)

     setmetatable(replace, { __index = function(t,k)
         t[k] = k
         return k
     end })


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