[Haskell-cafe] Why aren't there anonymous sum types in Haskell?
alexey.skladnoy at gmail.com
Tue Jun 21 22:57:49 CEST 2011
On 22.06.2011 00:32, pipoca wrote:
> On Jun 21, 4:15 pm, Alexander Solla<alex.so... at gmail.com> 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?
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