X了又Y，Y了又X: doing and undoing again and again
【高133】口语格式 / fixed patterns
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
X了又Y，Y了又X shows two actions that undo each other and alternate without end: 他把收音机装了又拆，拆了又装 ("he put it together, took it apart, put it together again, took it apart again…"). Only a turn and a half of the cycle is written, and the listener understands that it goes on. Each 了 says the previous action is finished before the other begins; 又 means "again".
The effect depends on the context: perseverance (写了又擦，擦了又写: the child is working at it), wasted effort (装了又拆) or hesitation (进了又出，出了又进). X and Y are usually opposite verbs (装/拆, 写/擦, 改/删, 买/退), and the two halves mirror each other: X then Y, Y then X. It is used in speech and in narrative alike.
Compare V来V去 (HSK 3): 想来想去 is a back-and-forth with no finished stages; here each step is complete before the next. Compare 又……又…… (HSK 2): 又高又瘦 describes two qualities at the same time, not two actions one after the other. And V了又V (看了又看, 想了又想) repeats the same verb: "look and look again".
Examples
我把那封信写了又撕，撕了又写，最后还是没寄出去。
Wǒ bǎ nà fēng xìn xiě le yòu sī, sī le yòu xiě, zuìhòu háishi méi jì chūqù.I wrote that letter and tore it up, wrote it again and tore it up again, and in the end I never sent it.
她在店门口进了又出，出了又进，就是下不了决心。
Tā zài diàn ménkǒu jìn le yòu chū, chū le yòu jìn, jiùshì xià bu liǎo juéxīn.She kept going into the shop and coming out again at the door, unable to make up her mind.
孩子写了又擦，擦了又写，终于把那个字写端正了。
Háizi xiě le yòu cā, cā le yòu xiě, zhōngyú bǎ nàge zì xiě duānzhèng le.The child wrote the character, rubbed it out, wrote it again, rubbed it out again, and finally got it neat.
他把那台旧收音机装了又拆，拆了又装，修了整整一天。
Tā bǎ nà tái jiù shōuyīnjī zhuāng le yòu chāi, chāi le yòu zhuāng, xiū le zhěngzhěng yì tiān.He put that old radio together and took it apart again and again, and spent a whole day repairing it.
这个方案定了又改，改了又定，到现在还没个准。
Zhège fāngàn dìng le yòu gǎi, gǎi le yòu dìng, dào xiànzài hái méi ge zhǔn.This plan has been fixed and changed, changed and fixed again, and still nothing is certain.
Common mistakes
✗ 装了又拆，拆又装了。 → ✓ 装了又拆，拆了又装。 (the two halves are symmetrical and 了 follows the verb directly, before 又).
✗ 装又了拆 → ✓ 装了又拆 (了 goes right after the first verb).
✗ 她高了又瘦 → ✓ 她又高又瘦 (X了又Y needs two successive actions; two simultaneous qualities are 又……又……).