Hi,
2011/2/10 Yitzchak Gale
Simon Peyton-Jones wrote:
"Generic Defaults"... will replace... the "Derivable type classes" stuff... in GHC 7.2 or 7.4... Please yell if you are a secret user of derivable type classes, so this change would discombobulate you.
Could you give us a preview of the parts of the syntax spectrum that will be gobbled up by this? That is a way that the change could affect even people who are not using the current generics.
As far as I understand, only the keyword "generic" will be taken. A new GHC.Generics module will define many new types with common names like `C` and `D`; these are used for the generic representation of datatypes in any module that enables -XGenerics, but there are no clashes unless the programmer explicitly imports GHC.Generics, so that should be ok.
For example, the old generics knocked a very nice bracket out of consideration for TH syntax. It also blessed the names of certain magical constructors, which can be good to know about even if the magic doesn't leak out of the generics world.
I remember there was some strange behavior with a type constructor `1` which was supposedly caused by the old generics (or was it syb?). Hopefully there will be nothing like that in the new mechanism. Cheers, Pedro
Thanks, Yitz