-- bisect xs target: leftmost insertion point in a sorted numeric list.
-- Python `bisect.bisect_left` semantics: returns i such that
-- xs[0..i] < target <= xs[i..]. Empty list returns 0; target greater than
-- every element returns len xs; on ties the leftmost index wins.
-- Caller owns the sortedness precondition - bisect does not validate it.
-- O(log N), so it replaces the O(N) `flt fn xs` + len cascade on sorted
-- input.
-- In-range: 4 lands between 3 and 5.
mid>n;bisect [1,3,5,7] 4
-- Before-first: 0 inserts at index 0.
before>n;bisect [1,3,5,7] 0
-- After-last: 9 inserts at the end.
after>n;bisect [1,3,5,7] 9
-- Duplicates: bisect_left returns the leftmost match (not the rightmost).
dup>n;bisect [1,2,2,2,3] 2
-- Empty list: insertion point is always 0.
empty>n;bisect [] 5
-- Exact-match in single-element list lands left of the equal element.
single-hit>n;bisect [5] 5
-- run: mid
-- out: 2
-- run: before
-- out: 0
-- run: after
-- out: 4
-- run: dup
-- out: 1
-- run: empty
-- out: 0
-- run: single-hit
-- out: 0