I'm just wondering if there is any generic exception that I can throw in case I don't want to create custom one for example in some simple scripts.

I'm looking for an exception that takes a single String as a reason.

As an example the NoMethodError, however it has a specific semantics and I want a generic one. https://hackage.haskell.org/package/base-4.16.0.0/docs/Control-Exception.html#t:NoMethodError

CodePudding user response：

It depends on exactly what you want to do.

If you want to throw an IO error then you can just call error, which generates an ErrorCall exception. You can optionally catch that in your main function and produce a more user-friendly error message. This is roughly equivalent to what most other programming languages provide in the way of exception handling.

If you have some non-IO computations which might fail at various stages (e.g. looking something up in a Map and not finding it) then you can use Either String as a quick-and-dirty exception monad. The equivalent of throwing an exception is Left.

To make Either String a bit more powerful you can import Control.Monad.Except. This introduces the MonadError typeclass, which includes Either as an instance. Hence by importing it you can use throwError and catchError.

Alternatively you can use the ExceptT monad transformer (also part of Control.Monad.Except) to add exceptions to any other monad you happen to be working with.