  lua-l archive

• Subject: Transform (cond ? then : else) to ifthenelse(cond, then, else) with lpeg
• Date: Mon, 20 Feb 2012 18:21:17 +0100

```Hello all,

I'm trying to convert a string like

'a?(b?c:d):e'

to another string

'ifthenelse(a,ifthenelse(b,c,d),e)'

using the lpeg lua parser. I'm slowly learning how to use lpeg but I
still can't find a suitable solution to do this with capture
substitutions. Any ideas?

Here is what I did so far.

local lpeg = require("lpeg")

local S, P, R = lpeg.S, lpeg.P, lpeg.R
local C, Cc, Ct = lpeg.C, lpeg.Cc, lpeg.Ct
local Cf, Cg, Cs = lpeg.Cf, lpeg.Cg, lpeg.Cs
local V = lpeg.V

local thenop = P("?")
local elseop = P(":")
local openpar = P("(")
local closepar = P(")")
local digit = R("09")
local letter = R("az") + R("AZ")

local parser =
P({
"F",
F = V("E") * (thenop * V("E") * elseop * V("E"))^0,
E = (letter + digit)^1 + (openpar * V("F") * closepar)
}) -- * -1 -- Is it needed?
print(lpeg.match(parser,"a?(b?c:d):e"))
print(lpeg.match(parser,"a"))

PS: This is a question I asked a few days ago here
http://stackoverflow.com/questions/9330477/transform-cond-then-else-to-ifthenelsecond-then-else-with-lpeg