[Haskell-cafe] Getting results of of runSTUArray

Henning Thielemann lemming at henning-thielemann.de
Wed Oct 20 12:53:18 EDT 2010

On Wed, 20 Oct 2010, Henry Laxen wrote:

> I am trying to do something that I think should be very simple, but I
> just can't seem to figure out how.  The idea is that I want to use
> runSTUArray to build up an array, but I want to look at the array
> after each iteration and possiblely accumulate some elements.

The result of runSTUArray is an immutable array, it cannot be altered 
anymore, only read and transformed to a new copy. Everything that modifies 
the array must happen inside runSTUArray.

If you want other things than an array out of the ST monad then use runST.

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