If : IfBlock
       | IfBlock ELSE COLON Terminator Block

def p_If(p):
    '''
    If : IfBlock
       | IfBlock ELSE COLON Terminator Block
    '''
    if len(p) == 2:
        p[0] = If(p[1], None, None)
    else:
        p[0] = If(p[1], p[5], p[4])