[mercurial]

You're right to some extent, but I think many of these 'knobs' have a good reason to exist (--dry-run, -a, -z for rsync for instance) and cannot be usefully, or at all, replaced by more composability. And attempting to implement support for them will run against the limitations of Haskell's syntax.

Something like OCaml would be better suited, since polymorphic variants, named and default arguments give a lot more flexibility, though the fact that shell commands happily return different outputs depending on their options would still be an issue.