If I understand your question correctly, no, it doesn't. Actually, the thing that you "unparse" doesn't even have to come from a regex matching to begin with. A

If I understand your question correctly, no, it doesn't. Actually, the thing that you "unparse" doesn't even have to come from a regex matching to begin with. As long as the type matches, everything is fine. If you are interested by unparsing, I would advise you to read the (famous) paper functional unparsing by Danvy[1]. The module Printf and Format of the OCaml standard library are basically this paper on steroid. I recently wrote a blog on part of the implementation technique[2]. Hope that helps. :) [1]: http://www.brics.dk/RS/98/12/BRICS-RS-98-12.pdf http://www.brics.dk/RS/98/12/BRICS-RS-98-12.pdf [2]: https://drup.github.io/2016/08/02/difflists/ https://drup.github.io/2016/08/02/difflists/ [Printf]: http://caml.inria.fr/pub/docs/manual-ocaml/libref/Printf.html http://caml.inria.fr/pub/docs/manual-ocaml/libref/Printf.htm... [Format]: http://caml.inria.fr/pub/docs/manual-ocaml/libref/Format.html http://caml.inria.fr/pub/docs/manual-ocaml/libref/Format.htm...