Concat as match pattern

Stream: Is there code for X?

[Daniel Weber]

Is there a way to use docs#SimpleGraph.Walk.concat as a match pattern, instead of cons?

[Yaël Dillies]

Do you mean [a] ++ p, [a, b] ++ p, etc..., rather than p ++ q (where p is a free variable)? For the former, the answer is yes and all you need to do is tag concat with @[match_pattern]. For the latter, the answer is no because p ++ q doesn't reduce to a constructor application.