Korean Grammar Dictionary

-ㄹ 걸 (그랬다) 【진작에 떴을 걸 [ edit | delete | edit examples ]
관용구/준꼴 Contraction (관용구/준꼴 Contraction)
『 』
Built on what Martin calls the accusative to "mark an antithetical clause that ends in a modifier + 것," and in origin, a contraction from -(으)ㄹ 것을 (그랬다): should have done; wish I had done; I wish I had ..., but I didn't ... (regretting lost opportunities); I should have (but I didn't).

진작에 떴을 걸 (삼포 6)
I should have left earlier

텃논의 참새를 봐야 할 걸 하는 생각이 든다 (소나기 )
The thought occurred to him that he should maybe/probably check on the sparrows in the rice paddy adjoining the house. (Here this pattern is quoted as a thought to oneself.)

용녀가 만약 말을 안 들으면 밤중에 내려가 가만히 업어올 걸 (산 8)
If by chance Yongnyŏ won't do as I say, I should just go down there in the middle of the night and take her away.