Puzzle #006: Rail Pool

This was the very first Rail Pool I constructed. In hindsight it’s not the most amazing puzzle, but it showcases a variety of basic logic in the genre and I just thought it would be neat to include it for… uh… “historical reasons” I guess.

Rules: Draw a non-intersecting loop through the centres of all cells. Some boldly outlined regions contain number clues. If a straight loop segment visits any cells of a clued region, its length must match one of these numbers. Each number must correspond to at least one such loop segment. Question marks represent any positive integer, but numbers cannot repeat within a region.