I think acid-state (<a href="http://hackage.haskell.org/package/acid-state">http://hackage.haskell.org/package/acid-state</a>) might do what you want, at least in broad strokes. It uses a durable transaction log to store query and update events. <div>

<br></div><div>As far as I know, the interface to the library doesn&#39;t expose an undo/rollback function, so you&#39;d have a bit of work to do to extend it to your use case. But the core functionality to make it possible should be there. </div>

<div><br></div><div>Can you use ghc extensions aside from Template Haskell? Template Haskell you can do without with acid-state, but without GADTs and so on you&#39;ll have problems.</div><div><br><div class="gmail_quote">

On Sun, Jan 6, 2013 at 12:01 PM, Casey Basichis <span dir="ltr">&lt;<a href="mailto:caseybasichis@gmail.com" target="_blank">caseybasichis@gmail.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">

<div dir="ltr">Hi,<br clear="all"><div><br></div>I am still getting a hang of Haskell.  Sorry if the answer is obvious.<div><br></div><div>What sorts of packages and approaches should I be looking at if I was looking to store something like an Undo stack into a database.</div>


<div><br></div><div>Each table would refer to a function. </div><div>Each records input and outputs would specify both a table ID and record ID.  </div><div>The records would also have a data and a Process ID to associate all functions to a specific process and give them an order.<br>


</div><div><br></div><div>No records are ever deleted.  Rolling something back is instead a process of recreating a new, modified graph by taking the old graph from the database.</div><div><br></div><div>I should note that while I can generate some of the boiler parts from template haskell in advance I&#39;m ultimately using a stage 1 compiler with no GHCI o template haskell.</div>


<div><br></div><div>Thanks,</div><div>Casey</div><span class="HOEnZb"><font color="#888888"><div><br></div>-- <br>Casey James Basichis<br>Composer - Cartoon Network<br><a href="http://www.caseyjamesbasichis.com" target="_blank">http://www.caseyjamesbasichis.com</a><br>


<a href="mailto:caseybasichis@gmail.com" target="_blank">caseybasichis@gmail.com</a><br><a href="tel:310.387.7540" value="+13103877540" target="_blank">310.387.7540</a>
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