Re: [Haskell-cafe] Are constructors strict?

loop = MonadPlus m => m Bool

loop = loop

If we apply Just to loop as follows

test2 :: MonadPlus m => m (Maybe Bool)

test2 = loop >>= return . Just

the evaluation of test2 does not terminate because >>= has to evaluate loop. But this does not correctly reflect the behaviour in a functional logic language like Curry. For example, if you have a function that checks whether the outermost constructor of test2 is Just, the test is supposed to be successful. In the naive model for non-determinism this is not the case.

Do I have to have MonadPlus m or would any other Monad class work the same way? -- Daryoush Weblog: http://perlustration.blogspot.com/