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<TITLE>Re: [Haskell-cafe] Multiple State Monads</TITLE>
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On 16/01/2009 01:28, "Luke Palmer" <lrpalmer@gmail.com> wrote:<BR>
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</SPAN></FONT></FONT><BLOCKQUOTE><BLOCKQUOTE><FONT SIZE="4"><FONT FACE="Calibri, Verdana, Helvetica, Arial"><SPAN STYLE='font-size:11pt'>Compile-time constants could be handled by simple top-level bindings. This technique is specifically for the case you are after:<BR>
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</FONT></SPAN><FONT FACE="Courier New"><SPAN STYLE='font-size:10pt'>mcSimulate :: Double -> Double -> Word64 -> [Double]<BR>
mcSimulate startStock endTime seedForSeed = go seedForSeed<BR>
</SPAN></FONT></FONT><FONT FACE="Courier New"><FONT SIZE="5"><SPAN STYLE='font-size:12pt'> </SPAN></FONT><FONT SIZE="4"><SPAN STYLE='font-size:11pt'>where<BR>
go = fst expiryStock : go newSeedForSeed<BR>
where<BR>
</SPAN></FONT><FONT SIZE="5"><SPAN STYLE='font-size:12pt'> </SPAN></FONT><FONT SIZE="4"><SPAN STYLE='font-size:10pt'>expiryStock = iterate evolveUnderlying (startStock, ranq1Init seedForSeed) <BR>
!! truncate (endTime/timeStep)<BR>
</SPAN></FONT><FONT SIZE="5"><SPAN STYLE='font-size:12pt'> </SPAN></FONT><FONT SIZE="4"><SPAN STYLE='font-size:10pt'>newSeedForSeed = seedForSeed + 246524<BR>
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</SPAN></FONT><SPAN STYLE='font-size:11pt'><FONT FACE="Courier New">See what's going on there?<BR>
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I don't know about that nested where. In Real Life I would probably use a let instead for expiryStock and newSeedForSeed.<BR>
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Luke<BR>
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Ahh, I get it now, that’s pretty neat - ‘go’ is only updating the seedForSeed and the expiryStock, the inner ‘where’ clause keeps everything else constant each time it is called.<BR>
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Thanks again!<BR>
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Phil.<BR>
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