Re: [Haskell-cafe] Using the ContT monads for early exits of IO ?

On 11 June 2010 10:12, Roman Cheplyaka wrote:

* Günther Schmidt [2010-06-11 01:22:27+0200]

...

there is nothing wrong with ifs as such except the won't actually exit a long piece of code, the computation will continue, just in a useless way.

Can you clarify?

I think Günther assumed that I was suggesting: do if x then return () else bar continueComputation The problem is that if 'x' is true, continueComputation should never happen. So you can solve it like this, which is what I was actually suggesting: do if x then return () else do bar; continueComputation But then you have this problem, which Günther addressed: 2010/6/11 Günther Schmidt :

Primarily for every "if" I need two forks, so at every "if" the branches double.

Which can be a big problem if you have a sequence of heterogenous actions that must be executed in order and are dependant and nested. Continutations solve this, as do ErrorT and MaybeT which are both restricted subsets for returning values. I'd use MaybeT if a value needed to be returned, or nothing.