[Haskell-cafe] wondering about a MonadIO instance for a heap data type

Eugene Kirpichov ekirpichov at gmail.com
Thu Jul 12 00:28:17 CEST 2012

Use Debug.Trace.
It does not make sense to declare that heap is a monad, as a monad is an abstraction of sequencing computations, and a heap is not an abstraction of sequencing computations at all. You don't make your String class implement the "rendering engine" interface just because you want to use it in a computer game program, equally you dont pretend that a heap is a way of sequencing computations just because you want to sequence computations related to heaps.

The actual computation in your case is the heapsort function, not the heap. If you absolutely must use IO, add IO to the functions type.

11.07.2012, в 15:19, Qi Qi <qiqi789 at gmail.com> написал(а):

> Hi,
> I was wondering about creating an instance of MonadIO for a heap data.
> Any hints?
> data Heap a = E | T Int a (Heap a) (Heap a)
>     deriving (Eq, Ord, Read, Show)
> The reason is that I want to use liftIO during a heapsort to print out
> intermediate results.
> Thanks.
> Qi Qi
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