Commutative dispatching #110

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1. mrocklin commented on Jun 17, 2020

   

   mrocklin

   on Jun 17, 2020

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   The dumb way to do this is the following:

   @dispatch((A, B), (B, A))
   def f(x, y):
       ...

   There may also be another way to do it (I'm no longer up to date on this library)
2. asmeurer commented on Jun 17, 2020

   

   asmeurer

   on Jun 17, 2020

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   Looking at the code, I don't think this is implemented. But I wonder if it can be done simply by subclassing Dispatcher like

   from itertools import permutations
   
   class CommutativeDispatcher(Dispatcher):
       def add(self, signature, func):
           for perm in permutations(signature):
               super().add(perm, func)

   and then also redefine dispatch to use CommutativeDispatcher.

   The dumb way to do this is the following:

   Does that work? I thought tuple meant union. So wouldn't that also define f(A, A) and f(B, B)?
3. mrocklin commented on Jun 17, 2020

   

   mrocklin

   on Jun 17, 2020

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   Does that work? I thought tuple meant union. So wouldn't that also define f(A, A) and f(B, B)?

   Yes, you're correct. So maybe you want ...

   @dispatch(A, B)
   @dispatch(B, A)
   def f(x, y):
       ...

   As you say, making a wrapper would not be hard.
4. asmeurer commented on Jun 17, 2020

   

   asmeurer

   on Jun 17, 2020

   Last edited by asmeurer

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   Yes, that's what I want. Except I don't want to type it twice for each type, because I know that f is always commutative.

   Actually, maybe it will be better make a wrapper at the dispatcher level, rather than Dispatcher.

   (I haven't tested this)

   def commutative_dispatcher(*types):
       def inner(f):
           for perm in permutations(types):
               f = dispatch(*perm)(f)
           return f
       return inner

   (functions that return functions don't compose so easily in Python. I think we need monads or something ;-)