ANNOUNCE: GHC version 7.4.1

Simon Peyton-Jones simonpj at
Fri Feb 3 10:31:00 CET 2012

|    =============================================================
|     The (Interactive) Glasgow Haskell Compiler -- version 7.4.1
|    =============================================================
|   * There is a new feature kind polymorphism (-XPolyKinds).
|     A side-effect of this is that, when the extension is not enabled, in
|     certain circumstances kinds are now defaulted to * rather than being
|     inferred.

Just to clarify, kind polymorphism is in 7.4, but it's not a fully-supported feature.  We already know there are bugs, and it's not even fully implemented (notably, you can't give a polymorphic kind *signature* yet).  

But, except in so far as they represent regressions, we won't push bug fixes into the 7.4 branch.   Please DO give kind polymorphism a try, and DO report bugs; but if you want the fixes you'll need to use the HEAD.

Why did we do it this way? Because implementing kind polymorphism entailed quite a bit of code upheaval. If we hadn't put that upheaval in the branch we'd have ended up fixing other bugs twice, once in the branch and once in the HEAD.


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