for (var i in o)
    if (o.hasOwnProperty(i)) {
        // have fun with o[i]
    }

function foo(bar){
	if(baz === undefined)
		return "nope";
}
foo();    // ReferenceError: baz is not defined

function foo(bar){
	if(typeof baz === "undefined")
		return "nope";
}
foo();    // "nope"

G = """
expr = factor ([+-] factor)*
factor = primary ([*/] primary)*
ident = [a-zA-Z_][a-zA-Z0-9_]*
number = [0-9]+
primary = "(" expr ")" / ident / number / "-" primary
"""

grammar(G).parse("5+3*5-(6+5)/3")

# Demo, simple calculator.
G = parse_grammar(r"""
expr = factor ([+-] factor)*
factor = primary ([*/] primary)*
number = [0-9]+
primary = "(" expr ")" / number / "-" primary
""")

def eval_expr(a):
    r = eval_factor(a[0])
    for f in a[1]:
        if f[0].str() == "+":
            r += eval_factor(f[1])
        else:
            r -= eval_factor(f[1])
    return r

def eval_factor(a):
    r = eval_primary(a[0])
    for p in a[1]:
        if p[0].str() == "*":
            r *= eval_primary(p[1])