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

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?