Re: [Haskell-cafe] Why aren't there anonymous sum types in Haskell?

On 22.06.2011 00:32, pipoca wrote:

On Jun 21, 4:15 pm, Alexander Solla wrote:

...

The problem is that a sum type must "name" the different types, or else it can't give access to them. How is a function supposed to know if a value

blah :: A :+: B

is an A or a B? It seems possible that it could figure it out, but that problem is undecidable in general.

Why can't you use pattern matching? We'd probably want to change the syntax a little, to tell Haskell that we want to use an anonymous sum.

Something like:

foo :: Bar :+: Baz -> Quux foo<Bar bar> = ... foo<Baz baz> = ...

Would finding the type signature of foo be undecidable?

Types may be same. oops :: Int :+: Int -> Int oops <Int i> = mmm which one?