Monads, again :)

[Leonardo Borges]

Digging through the source code of core.typed I found a namespace that guided me through successfully type checking the following:

  (t/cf (t/defalias MonadLB

          (t/TFn [[x :variance :covariant]] t/Nothing)))

  (t/cf (t/defprotocol [[M :variance :covariant,

                         :> MonadLB

                         :< Monad]]

          Monad

          ([a] return [mv :- (M a) v :- a] :- (M a))

          ([a b] bind [mv :- (M a) f :- [a -> (M b)]] :- (M b))))

Which seems reasonable. However, when I then try to type check a function that depends on this information, I get the error: 

"Type Error:  Internal Error: Lower-bound MonadLB is not below upper-bound Monad"

The offending function definition and annotation are as follows:

  (t/cf (ann  for-all-m (All [[f :< Monad] a]

                             [(f Boolean)

                              [a -> (f Boolean)]

                              (Option a)

                              -> (f Boolean)])))

  (t/cf (defn for-all-m [ctx p o]

          ((inst return f Boolean) ctx false)))

Thoughts?

Cheers

[Ambrose Bonnaire-Sergeant]

What happens if you omit the lower bound?

It's dumb that you have to provide it, but I remember why I now.

Thanks,

Ambrose

[Leonardo Borges]

Do you mean in the protocol definition like so?

(t/cf (t/defprotocol [[M :variance :covariant,

                         :< Monad]]

          Monad

          ([a]   return [mv :- (M a) v :- a]            :- (M a))

          ([a b] bind   [mv :- (M a) f :- [a -> (M b)]] :- (M b))))

This errors with:

Type Error : Internal Error : Could not resolve Protocol: myns.core/Monad