Jelly took a decent amount of inspiration from CJam when it comes to builtins (e.g. the idea of Æ prefix and Œ prefix come from CJam's m and e prefixes), and CJam (and Golfscript) both had ( and ) acting on arrays. ) on an array [1, 2, 3, 4, 5] pushes 1 and [2, 3, 4, 5] to the stack (and ( pushed [1, 2, 3, 4], 5 to the stack), i.e. modifying head/tail
CJam's way of "replacing" an array with it's head was 1= (or W= for tail), which is indexing, which makes even more sense
