ExceptT package:mtl-prelude

A monad transformer that adds exceptions to other monads. ExceptT constructs a monad parameterized over two things:
  • e - The exception type.
  • m - The inner monad.
The return function yields a computation that produces the given value, while >>= sequences two subcomputations, exiting on the first exception.
Convert a ExceptT computation to MaybeT, discarding the value of any exception.
Map the unwrapped computation using the given function.
Convert a MaybeT computation to ExceptT, with a default exception value.
The inverse of ExceptT.
Transform any exceptions thrown by the computation using the given function.