[Haskell-cafe] Library design question
lemming at henning-thielemann.de
Thu Sep 18 18:01:14 EDT 2008
On Thu, 18 Sep 2008, Andre Nathan wrote:
> On Thu, 2008-09-18 at 21:15 +0200, Henning Thielemann wrote:
>> Think of the state monad as processing a graph in-place. Which graph is
>> addressed is declared when running the State monad using runState or
> Interesting. Is it good practice then to do something like
> type GraphM a b = State (Graph a b)
> to hide from the user that I'm using the State monad underneath?
'type' won't hide anything but reduces writing. With 'newtype' you could
hide the State monad. You could do this, if you plan to change the
representation of a Graph to something based on mutable structures. On the
other hand with 'newtype GraphM' the user could not easily work on several
states of the graph simultaneously.
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