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local lpeg = require 'lpeg'
-- Lexical Elements
local Space = lpeg.S(" \n\t")^0
local Number = lpeg.C(lpeg.P"-"^-1 * lpeg.R("09")^1) * Space
local TermOp = lpeg.C(lpeg.S("+-")) * Space
local FactorOp = lpeg.C(lpeg.S("*/")) * Space
local Open = "(" * Space
local Close = ")" * Space
-- Auxiliary function
function eval (v1, op, v2)
if (op == "+") then return v1 + v2
elseif (op == "-") then return v1 - v2
elseif (op == "*") then return v1 * v2
elseif (op == "/") then return v1 / v2
end
end
-- Grammar
local V = lpeg.V
G = lpeg.P{ "Exp",
Exp = lpeg.Cf(V"Term" * lpeg.Cg(TermOp * V"Term")^0, eval);
Term = lpeg.Cf(V"Factor" * lpeg.Cg(FactorOp * V"Factor")^0, eval);
Factor = Number / tonumber + Open * V"Exp" * Close;
}
local test
if arg[1] then
local f = io.open(arg[1], 'r')
test = f:read '*a'
f:close()
else
test = [[10 + 5 * 2 + 10]]
end
print(lpeg.match(G, test))
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