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T20542.hs:17:7: error:
• Overlapping instances for Foo String String
arising from a use of ‘foo’
Matching instances:
instance [overlappable] Show a => Foo a String
-- Defined at T20542.hs:10:31
instance [overlapping] Read b => Foo String b
-- Defined at T20542.hs:13:30
An overlapping instance can only be chosen when it is strictly more specific.
The first instance that follows overlaps the second, but is not more specific than it:
instance [overlapping] Read b => Foo String b
instance [overlappable] Show a => Foo a String
• In the expression: foo
In an equation for ‘bar’: bar = foo
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