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T13292a.hs:4:12: warning: [-Wdeferred-type-errors (in -Wdefault)]
• Ambiguous type variable ‘m0’ arising from a use of ‘return’
prevents the constraint ‘(Monad m0)’ from being solved.
Relevant bindings include
someFunc :: m0 () (bound at T13292a.hs:4:1)
Probable fix: use a type annotation to specify what ‘m0’ should be.
These potential instances exist:
instance Monad IO -- Defined in ‘GHC.Base’
instance Monad Maybe -- Defined in ‘GHC.Base’
instance Monoid a => Monad ((,) a) -- Defined in ‘GHC.Base’
...plus three others
...plus two instances involving out-of-scope types
(use -fprint-potential-instances to see them all)
• In the expression: return ()
In an equation for ‘someFunc’: someFunc = return ()
T13292.hs:6:1: warning: [-Wdeferred-type-errors (in -Wdefault)]
• Couldn't match type ‘GHC.Types.Any’ with ‘IO’
Expected: IO ()
Actual: GHC.Types.Any ()
• In the expression: main
When checking the type of the IO action ‘main’
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