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<P><FONT SIZE=2 FACE="Arial">I'm doing some statistical calculations, and I decided to try this out in Haskell to see how it goes. I'm really enjoying using the language, so I hope I can straighten this out so I can keep using it at work.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">I keep getting stack overflows, so I think my code must be too lazy somewhere (that's what that means, right?) Here is my code to build random vectors and matrices.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">--------------------------------------------------------------------------------</FONT>
<BR><FONT SIZE=2 FACE="Arial">type Vector = UArray Int Float</FONT>
<BR><FONT SIZE=2 FACE="Arial">type Matrix = DiffArray Int Vector</FONT>
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<P><FONT SIZE=2 FACE="Arial">-- Generate a random number from the unit interval</FONT>
<BR><FONT SIZE=2 FACE="Arial">randomEntry :: State StdGen Float</FONT>
<BR><FONT SIZE=2 FACE="Arial">randomEntry = do g <- get</FONT>
<BR><FONT SIZE=2 FACE="Arial"> (x, g') <- return $ randomR (0,1) g</FONT>
<BR><FONT SIZE=2 FACE="Arial"> put g'</FONT>
<BR><FONT SIZE=2 FACE="Arial"> return x</FONT>
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<P><FONT SIZE=2 FACE="Arial">-- Build an array of n random things</FONT>
<BR><FONT SIZE=2 FACE="Arial">randomArray :: (IArray arr a) => Int -> State StdGen a -> State StdGen (arr Int a)</FONT>
<BR><FONT SIZE=2 FACE="Arial">randomArray n x = mapState arr . sequence $ replicate n x</FONT>
<BR><FONT SIZE=2 FACE="Arial"> where</FONT>
<BR><FONT SIZE=2 FACE="Arial"> arr (a,s) = (array (1,n) $ zip [1..n] a, s)</FONT>
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<P><FONT SIZE=2 FACE="Arial">-- A random vector is an array of random entries</FONT>
<BR><FONT SIZE=2 FACE="Arial">randomVector :: Int -> State StdGen Vector</FONT>
<BR><FONT SIZE=2 FACE="Arial">randomVector n = randomArray n randomEntry</FONT>
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<P><FONT SIZE=2 FACE="Arial">-- a random matrix is an array of random vectors.</FONT>
<BR><FONT SIZE=2 FACE="Arial">randomMatrix :: Int -> Int -> State StdGen Matrix</FONT>
<BR><FONT SIZE=2 FACE="Arial">randomMatrix i j = randomArray i $ randomVector j</FONT>
<BR><FONT SIZE=2 FACE="Arial">--------------------------------------------------------------------------------</FONT>
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<P><FONT SIZE=2 FACE="Arial">I decided to write a tester function to see whether building the random matrices is the root of my problem.</FONT>
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<P><FONT SIZE=2 FACE="Arial">tester :: Int -> [Matrix]</FONT>
<BR><FONT SIZE=2 FACE="Arial">tester n = fst $ runState vals $ mkStdGen 1</FONT>
<BR><FONT SIZE=2 FACE="Arial"> where </FONT>
<BR><FONT SIZE=2 FACE="Arial"> vals = sequence . repeat $ randomMatrix n n </FONT>
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<P><FONT SIZE=2 FACE="Arial">Then if I do</FONT>
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<P><FONT SIZE=2 FACE="Arial">main = print $ ((tester 10)!!10000)!5</FONT>
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<P><FONT SIZE=2 FACE="Arial">with ghc -O, I get a stack overflow. So all main is trying to do is build an infinite list of 10x10 random matrices, extract the 10000th one, and then look at row 5.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">Stack overflows like this have given me trouble before. I thought using unboxed arrays might help, since they're forced to be strict, but I haven't had any luck with them. Are there any general guidelines I'm overlooking? I think Haskell can be very useful in my work, but I have to get beyond this hurdle. I just figured out the State monad yesterday, so maybe I'm not using it as it's intended? I dunno.</FONT></P>
<P><FONT SIZE=2 FACE="Arial">Thanks,</FONT>
<BR><FONT SIZE=2 FACE="Arial">Chad Scherrer</FONT>
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