The interface is nicer for keyframe interpolation eg. the problem where you have a list of (X,Y) pairs and you want to find the two pairs that straddle a given

The interface is nicer for keyframe interpolation eg. the problem where you have a list of (X,Y) pairs and you want to find the two pairs that straddle a given x and interpolate between them. In that case, search(|&i| v[i].0 >= x, 0, v.len() - 1) handles the three cases "before the beginning", "after the end", and "between two pairs" fairly naturally.