[SkyMarshal]

TLDR:

> Pen is a statically typed functional programming language for application programming with system injection. Its design is heavily inspired by the Go programming language and many functional programming languages like Haskell and Koka.

... Pen aims to be even simpler [than Go] by ... removing several features from Go like pointers, mutability, method syntax, global variables, circular references, etc.

... Pen's approach to that [maintenance] is embracing battle-tested ideas in such field [software engineering], such as Clean Architecture, into the language's principles and ecosystem. One of its most clear incarnations is system injection.

System Injection: A mechanism to inject system functions into pure functions, eg a dynamically typed effect system (https://github.com/pen-lang/pen#system-injection)