To provide an example of the utility of method combinations:<p>I wrote a project skeleton generator[0] whose functionality is provided by progn-composable plugins, implemented as mixin classes.<p>Every bit of functionality, like adding a README.md file to a project skeleton, adding a .gitignore file, adding stub unit tests, etc. is implemented as a mixin class. A full template inherits[1] all the mixins it needs.<p>There is a generic function, render-template[1], that takes a template, some options, and the target directory, and uses the progn method combination. Meaning: every method in the chain is called in succession, and each method adds its own thing to the generated project. The render-template method for the gitignore mixin adds a .gitignore file,  for instance. When render template is called on an instance of a class that inherits a bunch of template mixins, it runs all of those mixins in addition to the render-template method of that class itself (if any).<p>In a sense, this is basically the entity-component pattern[3] implemented in the object system itself, with the caveat that you can&#x27;t have &quot;multiple instances&quot; of the same component -- you can&#x27;t inherit a class twice.<p>[0]: <a href="https:&#x2F;&#x2F;github.com&#x2F;roswell&#x2F;mystic" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;roswell&#x2F;mystic</a><p>[1]: <a href="https:&#x2F;&#x2F;github.com&#x2F;roswell&#x2F;mystic&#x2F;blob&#x2F;2d0fd8e401d50893b4a15f009dcd3958b7da5e57&#x2F;templates&#x2F;library&#x2F;library.lisp#L17" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;roswell&#x2F;mystic&#x2F;blob&#x2F;2d0fd8e401d50893b4a15...</a><p>[2]: <a href="https:&#x2F;&#x2F;github.com&#x2F;roswell&#x2F;mystic&#x2F;blob&#x2F;2d0fd8e401d50893b4a15f009dcd3958b7da5e57&#x2F;src&#x2F;mystic.lisp#L123" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;roswell&#x2F;mystic&#x2F;blob&#x2F;2d0fd8e401d50893b4a15...</a><p>[3]: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Entity_component_system" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Entity_component_system</a>