NOTE: Chibi provides portable implementation however, it requires a lot of other libraries to be imported. We should provide own compliant implementation.
I’m adding this for Gauche so I could add a note here (and hope it helps).
Chibi implementation only depends on srfi-130 (actually (chibi string) which is slightly different). (chibi monad environment) is very simple and can be pulled in. You can use the reference implementation for 130 but it won’t be as effective. To deal with (chibi string) once you haev srfi-130, have a look at https://github.com/vyzo/gerbil/blob/master/src/std/srfi/159/string.ss