.~ -package:universum package:stack

(.~) assigns a value to the target. It's the same thing as using (%~) with const:
l .~ x = l %~ const x
See set if you want a non-operator synonym. Here it is used to change 2 fields of a 3-tuple:
>>> (0,0,0) & _1 .~ 1 & _3 .~ 3
(1,0,3)