[Haskell-cafe] RebindableSyntax, ifThenElse, and pattern matching
cdsmith at gmail.com
Sun Feb 7 19:08:33 UTC 2016
In a custom prelude, I have written the following definitions:
data Truth = True | False
ifThenElse :: Truth -> a -> a -> a
ifThenElse True x _ = x
ifThenElse False _ x = x
(==) :: a -> a -> Truth
(==) = ...
I'm replacing Bool with my own Truth type. Clients will be built with
RebindableSyntax, so that they will use these definitions for desugaring.
However, if I write this:
f :: Text -> Text
f "r" = "rrr"
f other = other
I get a build error indicating that GHC expected the (==) operator to
return a value of type Bool, rather than Truth.
Shouldn't pattern matching desugar to use overloaded ifThenElse in these
situations? Or is it expected that use of GHC.Types.Bool is hard-coded
even with RebindableSyntax enabled?
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