Helper macro for writing concrete effect signatures about fused-effects HOT 4 CLOSED

I think you don't need Template Haskell for this but the same can be accomplished by using type families and data kinds:

type family StackEff (members :: [(* -> *) -> * -> *]) where
  StackEff '[] = Eff VoidC
  StackEff (m ': ms) = Eff (m (StackEff ms))

type family StackEffM (members :: [(* -> *) -> * -> *]) m where
  StackEffM '[] m' = Eff (LiftC m')
  StackEffM (m ': ms) m' = Eff (m (StackEffM ms m'))

-- 'Something' from @patrickt above
type Something = StackEff [StateC [Foo], ErrorC SomeException]

from fused-effects.

I’d argue that this isn’t an inappropriate leak of details. Your selection of a handler nails the computation down to a specific carrier, and thence semantics; that’s something consumers need to know about.

Further, this sort of specification is only necessary when you’re actually handling effects. In all other cases you can use Member constraints to abstract a computation over the carrier.

Finally, there isn’t in general a strong match between an effect and one specifically “blessed” carrier. Take Trace, for example.

If we want to be able to change the definitions or names of carriers without affecting consumers, we can always define type synonyms for them. But newtypes are cheap, so we won’t gain much by doing so in my opinion.

from fused-effects.

@patrickt: I’m going to close this out given the above, but feel free to reopen if necessary.

from fused-effects.

@robrix Very fair! And @JaSpa’s example of how to infer it is lovely. Let’s keep this closed.

from fused-effects.