How to use constrained functions with run* functions

[flip111]

An example with runError and runState

foo :: v -> Eff (State v : Error e : es) a -> Eff es (Either (CallStack, e) (a, v)) foo init_state f = runError (runState init_state f) -- This works with concrete type bar :: Eff (State v : Error e : es) a bar = undefined -- But with constraints there is a problem (see below) bar :: (State v :> es, Error e :> es) => Eff es a bar = undefined baz :: forall es. Eff es (Either (CallStack, String) (Int, Double)) baz = foo 0.0 bar

 • Overlapping instances for State v0 :> (State Double : Error String : es) arising from a use of ‘bar’ Matching instance: instance (e :> es) => e :> (x : es) -- Defined in ‘effectful-core-2.2.2.2:Effectful.Internal.Effect’ Potentially matching instance: instance [overlapping] e :> (e : es) -- Defined in ‘effectful-core-2.2.2.2:Effectful.Internal.Effect’ (The choice depends on the instantiation of ‘v0, es’ To pick the first instance above, use IncoherentInstances when compiling the other instance declarations) • In the second argument of ‘foo’, namely ‘bar’ In the expression: foo 0.0 bar In an equation for ‘baz’: baz = foo 0.0 bar | 115 | baz = foo 0.0 bar | ^^^ 

How can one use runState and friends and pass in functions that are constrained and use the :> operator? I don't know how to go from concrete to constrained, thus all functions that use baz also need to be rewritten to use concrete es type.

[arybczak]

You can either remove unused constraints from the signature of bar or use effectful-plugin for disambiguation.

[flip111]

Worked with the plugin, thank you!

constraint of bar is used because i left out the implementation which uses it