This BIG PATCH contains most of the work for the New Coercion Representation See the paper "Practical aspects of evidence based compilation in System FC" * Coercion becomes a data type, distinct from Type * Coercions become value-level things, rather than type-level things, (although the value is zero bits wide, like the State token) A consequence is that a coerion abstraction increases the arity by 1 (just like a dictionary abstraction) * There is a new constructor in CoreExpr, namely Coercion, to inject coercions into terms
Super-monster patch implementing the new typechecker -- at last This major patch implements the new OutsideIn constraint solving algorithm in the typecheker, following our JFP paper "Modular type inference with local assumptions". Done with major help from Dimitrios Vytiniotis and Brent Yorgey.
Type checking for type synonym families This patch introduces type checking for type families of which associated type synonyms are a special case. E.g. type family Sum n m type instance Sum Zero n = n type instance Sum (Succ n) m = Succ (Sum n m) where data Zero -- empty type data Succ n -- empty type In addition we support equational constraints of the form: ty1 ~ ty2 (where ty1 and ty2 are arbitrary tau types) in any context where type class constraints are already allowed, e.g. data Equals a b where Equals :: a ~ b => Equals a b The above two syntactical extensions are disabled by default. Enable with the -XTypeFamilies flag. For further documentation about the patch, see: * the master plan http://hackage.haskell.org/trac/ghc/wiki/TypeFunctions * the user-level documentation http://haskell.org/haskellwiki/GHC/Indexed_types The patch is mostly backwards compatible, except for: * Some error messages have been changed slightly. * Type checking of GADTs now requires a bit more type declarations: not only should the type of a GADT case scrutinee be given, but also that of any identifiers used in the branches and the return type. Please report any unexpected behavior and incomprehensible error message for existing code. Contributors (code and/or ideas): Tom Schrijvers Manuel Chakravarty Simon Peyton-Jones Martin Sulzmann with special thanks to Roman Leshchinskiy
Update lhs-boot files A consequence of my recent meddling with hs-boot files is that GHC is more picky about the correpondence between the hs-boot file and the hs file. In particular, you must use the same type synonyms. This patche fixes up GHC's own hs-boot files to match the restriction.
Reorganisation of the source tree Most of the other users of the fptools build system have migrated to Cabal, and with the move to darcs we can now flatten the source tree without losing history, so here goes. The main change is that the ghc/ subdir is gone, and most of what it contained is now at the top level. The build system now makes no pretense at being multi-project, it is just the GHC build system. No doubt this will break many things, and there will be a period of instability while we fix the dependencies. A straightforward build should work, but I haven't yet fixed binary/source distributions. Changes to the Building Guide will follow, too.