#15710: Should GHC accept a type signature that needs coercion quantification? -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.6.1 Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Tupling: yes `f :: (Num a, Ord a) => blah` is ''already'' syntactic sugar for `f :: Num a => Ord a => blah`. But I'm more concerned about {{{ type C a b = (Num a, a ~ b) }}} and here it'd be much trickier (and unprincipled) to switch to unboxed tuples. Moreover, we do lots of constraint abstraction {{{ data Dict c where Dict :: c => Dict c }}} and we can't instantiate that polymorphic `c` with an unboxed tuple. So yes, I think we could have `Constraint` and `Constraint#` just as we have `Int` and `Int#`. But it's very uncomfortable to have to use `a ~# b` in a type if (but only if) the constraint is used in a dependent way. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15710#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler