#1968: data family + GADT: not implemented yet
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Reporter: Remi | Owner: chak
Type: bug | Status: new
Priority: normal | Milestone: 6.10 branch
Component: Compiler (Type checker) | Version: 6.9
Severity: normal | Resolution:
Keywords: data type family GADT choose_univs | Difficulty: Moderate (1
day)
Testcase: | Architecture: Multiple
Os: Multiple |
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Comment (by chak):
Yes, as Simon says, you are perfectly right about the three examples.
Just as a final remark on that topic, the reason why it is tempting to
think that "naming" a parameter in a `data family` declaration makes a
difference is because it '''does''' make a difference for a `type family`.
This is a point where data families and type synonym families are
fundamentally different. The underlying type theoretic rational derives
from the fact that a data family always introduces a '''new''' type,
whereas a synonym family doesn't. A secondary consequence is that data
families may be applied partially, whereas a synonym family must always be
applied to at least as many type arguments as its arity (i.e., the number
of named parameters in the declaration).
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/1968#comment:7>
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