On Tue, 11 Mar 2014 19:41:57 +0000, Semen Trygubenko / Семен Тригубенко
On Tue, Mar 11, 2014 at 01:21:01PM +0100, Niklas Haas wrote:
The idiomatic way to handle this kind of stuff normally is to pass an abstract proxy that carries the type as a type argument, rather than passing a value of that type itself, eg.:
data Proxy a = Proxy
dataTypeOf :: Data a => Proxy a -> DataTypeOf
or even a more polymorphic version:
dataTypeOf :: Data a => f a -> DataTypeOf
Thank you for your reply — I've read it many times, but couldn't translate it into code as of yet.
I don't mind ugly as long as it's safe. Specifically, how am I to construct an entity of type DataType (see Data.Data; DataType needs to be fed into readConstr) with the help of a wrapper function you are describing?
If someone could in the direction of a skeleton for such a function I might be able to fill in the gaps on my own. But currently I'm stuck… :/
Thanks again, S.
Oops, sorry, that was supposed to have been:
dataTypeOf :: Data a => Proxy a -> DataType or dataTypeOf :: Data a => p a -> DataType
As for the implementation, the simplest possible (ie. no language extensions) implementation I can think of looks like this:
dataTypeOf = Data.dataTypeOf . f where f :: p a -> a f _ = error "dataTypeOf: this should never be used"
where Data.dataTypeOf refers to the ‘original’ version of that function.