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|
-------------------------------------------------------------------------------
--
-- A preprocessor which uses Leg to transform ...[<exp>] into
-- select(<exp>, ...).
--
-- Author: Humberto Anjos
--
-- $Id: vararg-indexing.lua,v 1.2 2007/11/19 13:34:47 hanjos Exp $
--
-------------------------------------------------------------------------------
-- ye olde imports
local lpeg = require 'lpeg'
local parser = require 'leg.parser'
-- some aliasing to save my poor fingertips
local V, P, Cs = lpeg.V, lpeg.P, lpeg.Cs
-- argument processing
local args = { ... }
-- the code to parse
subject = args[1] or [=[
local arg1, arg2, arg3 = ...[1], ... [ -2 +x[[whatever, man]]^t[5] ], ...
-- Oh my G0dZ, a comment in the middle !!1!one!1! This will disappear
[-(-3)]
if do_or_die() then -- inside a block
return ...[BOOM_baby(...[2], 'boink!')] -- inside an expression
end
-- ...['inside a comment']
a = " ...['inside a string!'] "
]=]
-- spacing rule
local S = parser.rules.IGNORED -- scanner.IGNORED or V'IGNORED' could be used
-- a pattern which matches any instance of ...[<exp>] and returns
-- 'select(<Exp>, ...)'. You need parser.apply because the definition of Exp is
-- recursive, and needs roughly half of Lua's grammar to work. One could try to
-- work out which rules are actually needed, but just using the whole damn
-- thing is so much easier...
local oldExp = parser.rules.Exp
local VARARG = P( parser.apply (
{ -- the rule table
-- matching ...[<exp>]. We'll use lpeg.Cs for the substitution.
VarargIndex = V'...' *S* V'[' *S* V'Exp' *S* V']',
-- VarargIndex is now a valid subexpression. Using lpeg.Cs ensures that
-- inner VarargIndexes will be substituted as well. VarargIndex must be
-- matched before oldExp or the ... will be understood as a normal
-- ellipsis.
Exp = Cs(V'VarargIndex' + oldExp),
},
{ -- the capture table
VarargIndex = function (exp)
return 'select('..exp..', ...)'
end
}) )
-- a pattern which does the substitution with Cs
local ALL = Cs(VARARG)
-- printing the results
print('subject:', '\n'..subject)
print('result:', '\n'..ALL:match(subject))
|
