Toy calculator in Lua, version 1

hoc1.lua

function eval(num1, operator, num2)
    if operator == '+' then
        return num1 + num2
    elseif operator == '-' then
        return num1 - num2
    elseif operator == '*' then
        return num1 * num2
    elseif operator == '/' then
        return num1 / num2
    else
        return num1
    end
end

spc = lpeg.S(" \t\n")^0

number = spc * lpeg.C(
           lpeg.P('-')^-1 *
           lpeg.R('09')^0 *
           ( lpeg.P('.') *
             lpeg.R('09')^0
           )^-1 ) * spc /
         tonumber

expr = lpeg.P{
    "EXPR";
    EXPR = ( lpeg.V("TERM") * lpeg.C( lpeg.S('+-') ) * lpeg.V("EXPR") +
                 lpeg.V("TERM") ) / eval,
    TERM = ( lpeg.V("FACT") * lpeg.C( lpeg.S('/*') ) * lpeg.V("TERM") +
                 lpeg.V("FACT") ) / eval,
    FACT = ( spc * "(" * lpeg.V("EXPR") * ")" * spc +
                 number ) / eval
}

function repl(file)
    file = file or io.input()
    parser = expr
    for line in file:lines() do
        print(parser:match(line))
    end
end