[Haskell-cafe] sizeOf on a type

[Henning Thielemann]

On Fri, 18 Dec 2009, Gregory Crosswhite wrote:

> Yay, advancePtr is exactly what I needed!  I totally missed that one in the docs.
>
> Also thanks to those of you who pointed me to the scoped type variables 
> feature, since I had figured that a feature liked that had to exist but 
> I just didn't know where to look for it.

You do not need the Scoped Type Variables feature here, although it may 
simplify writing. I remember we had a similar thread here, recently. A 
solution can be:

sizeOfPtr :: Ptr a -> a -> Int
sizeOfPtr _ x = sizeOf x

to be called by (sizeOfPtr ptr undefined).

I have added this example to:
  http://www.haskell.org/haskellwiki/Scoped_type_variables#Avoiding_Scoped_Type_Variables

But in order to be found in Category:FAQ we might need a different title.