Re: Transform (cond ? then : else) to ifthenelse(cond, then, else) with lpeg

[William Ahern <william@...>]

On Mon, Feb 20, 2012 at 06:21:17PM +0100, Christophe Jorssen wrote:
> 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?

local lpeg = require("lpeg")

lpeg.locale(lpeg)

local function tr(a, b, c)
	if not b then
		return a
	else
		return string.format("ifthenelse(%s,%s,%s)", a, b, c)
	end
end

local var = lpeg.C(lpeg.alpha * (lpeg.alnum^0))

local E, G = lpeg.V"E", lpeg.V"G"

local grammar = lpeg.P{ "E",
	E = ((var + G) * (lpeg.P"?" * E * lpeg.P":" * E)^-1) / tr,
	G = lpeg.P"(" * E * lpeg.P")",
}

print(lpeg.match(grammar, "a?(b?c:d):e"))