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More Motivation For The Skeptical

There are so many CLI parser frameworks out there...Why do we need yet another?

This approach to command-line interfaces has some obvious Don't Repeat Yourself ("DRY", or relatedly "a few points of edit") properties. It also has very nice "loose coupling" properties. cligen need not even be present on the system unless you are compiling a CLI executable. Similarly, wrapped routines need not be in the same module, modifiable, or know anything about cligen.

This approach is great when you want to maintain an API and a CLI in parallel. Mostly you can just update the API and a single line of help message. Easy dual API/CLI maintenance encourages preserving access to functionality via APIs/"Nim import". When so preserved, this then eases complex uses being driven by other Nim programs rather than by shell scripts (once usage complexity makes scripting language limitations annoying).

Finally, and perhaps most importantly, this approach is "DRY for the brain". The learning curve/cognitive load and even the extra program text for a CLI is all about as minimal as possible. Any potential CLI author already knows the syntax for a Nim proc declaration with default values which serves as the "declarative specification language" for the CLI in cligen. Mostly they just need to learn what kind of proc is "command-like enough", various minor controls/arguments to dispatch to enhance the help message, and the "binding/translation" between proc and command parameters. The last is helped a lot by the auto-generated help message and all the controls are gradual and rather "pickyness-driven". So, there is a mentally pay-as-you-go/only-pay-for- what-you-use kind of property.