On Nov 19, 2007, at 16:50 , Henning Thielemann wrote:
On Mon, 19 Nov 2007, Brandon S. Allbery KF8NH wrote:
fromEnum and/or toEnum are helpful for this kind of thing, and I am occasionally tempted to bind "cast = toEnum . fromEnum" because I need it so much.
Really? I'd like to know which examples these are. So far I suspected that 'cast' indicates not well chosen types.
If so, it's not my types... The specific instance is the one you mentioned about times; fromEnum lets me turn a Foreign.C.Types.CTime (== System.Posix.Types.EpochTime) to an Int (which is commonly just type punning in GHC, since it's the same internal value representation in most (all?) cases), from which I can get to another Foreign.C.Types type with toEnum or to Integer with fromIntegral. (NB: This involves an assumption about CTime; POSIX allows (or used to allow) it to be a floating type in order to allow some non- UNIXlikes to represent POSIX times. But given that CTime is Enum, Foreign.C.Types already violates this; so why isn't it also Integral?) So yes, this is a sign of typing issues in the implementation and (toEnum . fromEnum) is a hack around them. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH