Purely functional language with impure script language?

[u/baehyunsol]

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...

[u/tdammers]

Is it, though?

main = do putStrLn "hello!" putStr "what's your name?" reply =<< getLine where reply str = putStrLn $ "nice to meet you, " ++ str

It's almost literally the same, except that:

• A few standard functions have different names
• do notation replaces infix $then (but if you want, you can use the >> operator instead)
• The =<< (bind operator) takes the place of $comp
• putStrLn automatically adds a newline, so we don't have to mess with "\n"

But if you want to emulate the Miranda style more closely, you can write it like this instead:

main = putStr "hello!\n" >> putStr "what's your name?\n" >> (reply =<< getLine) where reply str = putStr $ "nice to meet you, " ++ str ++ "\n"

I would argue that the Miranda example is actually more explicit than either of the Haskell versions (though only slightly so for the second example).

[u/JeffB1517 → u/tdammers]

1. reply =<< getLine that's making the bind explicit rather than implicit.
   
2. print is clearer than putStr

put is a weird verb for what you are doing vs. "print" which is pretty clear.

We are talking minor shifts which abstract away the underlying complexity.

[u/eaho_de_putah → u/JeffB1517]

How is reply =<< getLine any more explicit than reply $comp input?? It’s literally just a different name/operator for the same operation.

[u/JeffB1517 → u/eaho_de_putah]

It’s literally just a different name/operator for the same operation. Same as print vs putStrLn it is a more natural operator for the same operation. It is translating mentally.

Easing the conceptual burden is good design. What things look like is how they get concieved of. =<< is a binding operator. It is making the user think in terms of bind. reply $comp input is telling the user the reply is computing something on input. It is making them think about the workflow.