RepPolyMcBind.hs:26:16: error: [GHC-55287]
    • The first argument of the rebindable syntax operator ‘(>>=)’
        arising from a statement in a monad comprehension
      does not have a fixed runtime representation.
      Its type is:
        ma0 :: TYPE c0
      Cannot unify ‘rep’ with the type variable ‘c0’
      because it is not a concrete ‘RuntimeRep’.
    • In a stmt of a monad comprehension: x <- undefined :: ma
      In the expression: [() | x <- undefined :: ma]
      In an equation for ‘foo’: foo _ = [() | x <- undefined :: ma]
    • Relevant bindings include
        foo :: () -> ma (bound at RepPolyMcBind.hs:26:1)