id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
5830	Arrow if/then/else sugar breaks type inference	jamey		"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."	bug	closed	normal		Compiler	7.0.4	fixed		josh	Unknown/Multiple	Unknown/Multiple	GHC rejects valid program	Unknown