Shorter syntax for pattern matching function definitions

[MichalMarsalek]

Can we have something like:

def factorial(0) = 1
pdef factorial(n) = n * factorial(n - 1)

as a syntactic sugar for

def factorial(0) = 1

@addpattern(factorial)
def factorial(n) = n * factorial(n - 1)

so that it's closer to Haskell way of defining a function with multiple patterns?
Honestly, having to put @addpattern(function_name) before each definition kind of discourages me from doing it this way, instead of something like
factorial = n -> n*factorial(n-1) if n else 1
Of course factorial is just an example and pdef could be something entirely different.

[evhub]

I'd like to add this, but I'm not sure what the right syntax should be. pdef is nice and short, but not very informative. pattern def matches async def or match def, though it's a bit weird since pattern isn't a keyword on its own and it's somewhat long. Thoughts?

Also we'll want to make sure match pdef (or whatever) raises an error, since pdef should imply match def.

[MichalMarsalek]

I don't know, what you wrote are good points.

[eindiran]

I like the pattern def syntax. It matches with async def and match def quite well. The difference between the old Python 3.4 syntax

@asyncio.coroutine
def some_function():
    ...

and the modern async def is analogous to the long form syntax and the proposed new syntax.

Regarding your point that pattern is not its own keyword, that matches how async is used with with or def.

The keyword pattern is a bit long, but being clear and informative makes typing a few more characters worth it for almost anything than isn't code golfing.

[evhub]

This has now been implemented in coconut-develop as addpattern def!