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