aboutsummaryrefslogtreecommitdiff
path: root/src/Binary.hs
diff options
context:
space:
mode:
authorross <unknown>2003-04-25 10:50:06 +0000
committerross <unknown>2003-04-25 10:50:06 +0000
commiteb12972c9b217d46397791c63d19c418b1a3c83f (patch)
tree2a9cd6bbbbb68ac69bd3991f9486f09a6a8108dd /src/Binary.hs
parent6be4db86fa1f4a913db1e4703148edc83dc325e5 (diff)
[haddock @ 2003-04-25 10:50:05 by ross]
An 80% solution to generating derived instances. A complete solution would duplicate the instance inference logic, but if a type variable occurs as a constructor argument, then we can just propagate the derived class to the variable. But we know nothing of the constraints on any type variables that occur elsewhere. For example, the declarations data Either a b = Left a | Right b deriving (Eq, Ord) data Ptr a = Ptr Addr# deriving (Eq, Ord) newtype IORef a = IORef (STRef RealWorld a) deriving Eq yield the instances (Eq a, Eq b) => Eq (Either a b) (Ord a, Ord b) => Ord (Either a b) Eq (Ptr a) Ord (Ptr a) (??? a) => Eq (IORef a) The last example shows the limits of this local analysis. Note that a type variable may be in both categories: then we know a constraint, but there may be more, or a stronger constraint, e.g. data Tree a = Node a [Tree a] deriving Eq yields (Eq a, ??? a) => Eq (Tree a)
Diffstat (limited to 'src/Binary.hs')
0 files changed, 0 insertions, 0 deletions