I hear they are good, make it easier to maintain code-bases. Most often I reach for python to get the job done. Does anyone have experiences with functional languages for larger projects?
In particular I am interested to learn more on how to handle databases, and writing to them and what patterns they come up with. Is a database handle you can write to not … basically mutable state, the arch-nemesis of functional languages?
Are functional languages only useful with an imperative shell?
There can be, although some parts may still need to be written in assembly (which is imperative, because that’s ultimately what most CPUs do), for parts like a kernel’s context switching logic. But C has similar restrictions, like how it is impossible to start a C function without initializing the stack. Exception: some CPUs (eg Cortex M) have a specialized mechanism to initialize the stack.
As for why C, it’s a low-level language that maps well to most CPU’s native assembly language. If instead we had stack-based CPUs – eg Lisp Machines or a real Java Machine – then we’d probably be using other languages to write an OS for those systems.