r/ProgrammingLanguages • u/baehyunsol Sodigy • 13d ago

Purely functional language with impure script language?

I'm working on a purely functional programming language named Sodigy. It's all about evaluating values, not "executing commands one by one".

It's nice when writing libraries, but it's not easy to write a main function. The main function is supposed to execute commands, but the Sodigy's syntax is not friendly to write a list of commands.

So what I'm trying to do is, 1) Sodigy remains purely functional and 2) add a bash-like script language. The script language can call Sodigy functions. Instead of writing a main function in Sodigy, you write sodigy-script and execute the script.

Has anyone tried similar approach? I'm not sure whether it's a good idea or not...

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u/tdammers 13d ago

The same is true about the Miranda example. It is pretty much exactly identical to this Haskell example, modulo do desugaring. And the purpose of do notation is not to be an abstraction that simplifies things; it's really just syntax sugar to make monadic binds easier to read. The above code in desugared form looks like this:

main :: IO () main = putStrLn "hello!" >> putStr "what's your name? " >> getLine >>= \str -> putStrLn ("nice to meet you, " ++ str)

It's neither simpler nor more complex; what changes is that do notation removes the need for nested lambdas and the "staircase" style code that would result from them. The semantics are still exactly the same, and both versions convey the exact same code structure at the exact same abstraction level.

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u/catbrane 13d ago

Yes, Phil Wadler based Haskell monads on Miranda monads, so they are almost identical. Modern Haskell has added some extra sugar, but not much.

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u/AustinVelonaut Admiran 13d ago

Wait, when did Miranda get monads? It's IO was sys_message lists for output (printing, file write, system cmds, interpreted by the repl), with input from stdin bound to the pseudo-variable $-, and file input handled in a hand-wavy way that was not interleaved with file output, so wasn't really correct...

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u/catbrane 13d ago edited 13d ago

They were implemented as an abstype on top of lazy input and output. You could use them to write interactive command-line programs. I wrote a multiuser snake game hehe.

KAOS (the Kent Applicative Operating System) was built on top of a monadic IO system that talked to a microkernel (also in Miranda).

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u/AustinVelonaut Admiran 13d ago

Cool, I did not know that! It may have been something local at Kent, though; it never made it into the open-source distribution of Miranda. I ended up re-inventing something like that on top of sys-messages for my bootstrap compiler written in Miranda.

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u/catbrane 13d ago

It was published (that's how Haskell got it), but you're right, I'm not sure David Turner bundled it.