[Haskell-cafe] Use of the Try typeclass

Edward Z. Yang ezyang at MIT.EDU
Wed Dec 30 20:52:06 EST 2009

Hello all,

I am currently playing with the new cadre of failure libraries, and I'm
trying to figure out how to use the monadic version of Failure while
also getting the Try typeclass, which appears to be the standardized mechanism
for marshalling values from specific monads into the failure monad.
Unfortunately, it only seems to be defined when I import Control.Failure,
and this module is fairly incompatible with Control.Monad.Failure, as
demonstrated by this GHCI transcript:

    ezyang at javelin:~/Documents/tmr$ ghci
    Prelude> :m +Control.Failure
    Prelude Control.Failure> :m +Control.Monad.Failure
    Prelude Control.Failure Control.Monad.Failure> :t failure

        Ambiguous occurrence `failure'
        It could refer to either `Control.Failure.failure', imported from Control.Failure
                              or `Control.Monad.Failure.failure', imported from Control.Monad.Failure

I'm using MTL, which might be the reason why there's all sorts of unhappiness. :-)


More information about the Haskell-Cafe mailing list