IfBlock : IF Expression COLON Terminator Block
            | IfBlock ELIF Expression COLON Terminator Block

def p_IfBlock(p):
    '''
    IfBlock : IF Expression COLON Terminator Block
            | IfBlock ELIF Expression COLON Terminator Block
    '''
    if isinstance(p[1], str):
        p[0] = IfBlock(None, p[2], p[4], p[5])
    else:
        p[0] = IfBlock(p[1], p[3], p[5], p[6])