Arrow if/then/else sugar breaks type inference

Starting in GHC 7.0, using the Arrows if/then/else syntactic sugar for ArrowChoice doesn't propagate type constraints the way I expect. This bug still exists in 7.2.

The expected type of the result of the conditional should constrain the type of each branch of the conditional. Instead, the branches remain unconstrained. If the arrow in the branches is polymorphic and its argument type doesn't completely constrain its result (I used "read" in this test case) then GHC reports that the types are ambiguous:

     Ambiguous type variable `c0' in the constraint:
       (Read c0) arising from a use of `read'

Using the case-expression sugar instead works fine.

Trac metadata

Trac field	Value
Version	7.0.4
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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CC	josh
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