Sweet! Similar to docopt. It&#x27;s humbling to see how short this can be in Haskell, compared to my C++ code <a href="https:&#x2F;&#x2F;github.com&#x2F;ridiculousfish&#x2F;docopt_fish" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;ridiculousfish&#x2F;docopt_fish</a> (though in my defense the C++ version is more featureful, with better error messages).<p>We&#x27;re likely to build this sort of thing in directly to the fish shell: <a href="https:&#x2F;&#x2F;github.com&#x2F;fish-shell&#x2F;fish-shell&#x2F;issues&#x2F;478" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;fish-shell&#x2F;fish-shell&#x2F;issues&#x2F;478</a> . From a usage spec, you get tab-completions, syntax highlighting, argument parsing and validation, and user help.<p>It&#x27;s sort of silly that there is no machine-parseable usage spec for common Unix commands. Once the docopt support is integrated, I hope to create a repository of usage specs that anyone can contribute to, similar to explainshell.com