[Haskell-cafe] Re: Doing without IORef

Bryan O'Sullivan bos at serpentine.com
Fri Apr 4 12:56:35 EDT 2008

Jinwoo Lee wrote:

> I haven't used ReaderT. What are the advantages when using ReaderT
> instead of StateT in this case?

A StateT lets you replace one IORef with another, since it gives you
mutable state.  A ReaderT gives you *immutable* state, so the type
system guarantees that you'll always be using the same IORef.


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