The numeric c types are (effectively) integral, too.

Jeff Shaw shawjef3 at
Wed Mar 27 17:08:37 CET 2013

On Wednesday, March 27, 2013 11:30:24 AM, Henning Thielemann wrote:

> Writing orphan instances is generally a bad idea. Instead you could
> put your roundTo function into a nice package and import it
> everywhere.

Yup! So let's put the Integral, etc. instances right in 
Foreign.C.Types. That way no one will make the mistake you're accusing 
me of.

> I don't think that an Integral instance is the right way
> to go, since it would imply the signature:
> div :: CTime -> CTime -> CTime
> and the quotient of two time values is not a time.

That is irrelevant. CTime is a newtype of an integer type, and the 
quotient of two integers is an integer. Foreign.C.Types certainly 
doesn't have a problem dividing even stranger things, like graphemes by 

I'm quite sure that the reason that CTime doesn't have an Integral 
instance is that technically the C spec allows time_t to be a float. 
However, since time_t is practically always an integer value, we should 
expose that by defining the Integral instance right in Foreign.C.Types.

I looked through the header files for FreeBSD's platforms, and time_t 
is always an __int32 or __int64. Maybe Linux or NetBSD can provide an 


More information about the Libraries mailing list