Sorting a slice by one field is easy. Filtering one collection is easy. Returning (T, bool) is idiomatic. So is writing a nested loop. The friction appears when the same ordering must be shared by a stable sort and an extrema operation, a filter must be reused across several APIs, or a nested traversal grows into four nearly identical loops. At that point, the code is still simple locally, but the semantics are scattered across call sites. Shuttle is an attempt to give those semantics ...