~ $ racket -I rhombus Welcome to Racket v8.13 [bc]. > fun is_sorted(list): match list: | []: #true | [_]: #true | [head,

~ $ racket -I rhombus Welcome to Racket v8.13 [bc]. > fun is_sorted(list): match list: | []: #true | [_]: #true | [head, next, ...]: head .<= next && is_sorted([next, ...]) ; readline-input:6:19: next: cannot use repetition binding as an expression ; in: next ; [,bt for context] From there I got to "repetition binding" in the docs: https://plt.cs.northwestern.edu/pkg-build/doc/rhombus/Repetitions.html https://plt.cs.northwestern.edu/pkg-build/doc/rhombus/Repeti... From what I can understand, the "..." isn't independent of the previous expression in the list (as I would have expected from e.g. Prolog or Haskell). Instead you are defining a kind of pattern to reuse later, so tail gives a name to the rest of the list (so that it doesn't get associated with next).