-- lst xs i v: return a new list with element at index i replaced by v.
-- Value-semantics: the original list is unchanged. Out-of-range is a runtime
-- error on tree/vm engines (cranelift returns the list unchanged).
--
-- This replaces user-space rebuild loops for "increment bin i" patterns that
-- previously rebuilt the entire list on every update.
hist samples:L n bins:L n>L n;@s samples{c=at bins s;bins=lst bins s +c 1};bins
-- run: hist [0,2,1,2,3,1,2,0] [0,0,0,0]
-- out: [2, 2, 3, 1]
-- run: hist [1,1,1] [0,0]
-- out: [0, 3]