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    <blockquote> <p>What's likely to be the source of the problem? I have a few guesses (in decreasing order of likelihood):</p> </blockquote> <ul> <li>Formatting each Int32 with my code is inefficient.</li> </ul> <p>So-so. I'm not sure how well GHC optimises <code>shift x (-24)</code>, maybe using <code>shiftR x 24</code> is better, but I need to look at the generated core to know. Edit: perfectly fine, produces <code>uncheckedIShiftRA#</code>, as one could hope for.</p> <ul> <li>mapM_ over the array with (!) inefficient.</li> </ul> <p>Yes, a bit. Using <code>elems</code> or <code>unsafeAt</code> is slightly faster due to the omission of bounds-checks.</p> <ul> <li>Calling hPutStr a million times is inefficient.</li> </ul> <p>Definitely. But has less impact than I thought.</p> <ul> <li>1 minute to print 1 million values actually is efficient.</li> </ul> <p>No:</p> <pre><code>Prelude&gt; writeFile "IntList.txt" $ unlines . map show $ [1 :: Int .. 1048576] (0.37 secs, 836888976 bytes) </code></pre> <p>It's far more efficient - and may well be more efficient than using an intermediate <code>ByteString</code> - to produce one long <code>String</code> which is printed to the handle at once. The String will be lazily generated, so it will not use much memory, and the generating of the <code>String</code> is pretty efficient (still tweakable if need be).</p> <p>Going off to measure now.</p> <p>Using</p> <pre><code>printArray handle frozenArray = hPutStr handle $ showit (elems frozenArray) where showit :: [Int32] -&gt; String showit (n:ns) = (' ' :) . shows ((n `shiftR` 24) .&amp;. 255) . (' ' :) . shows ((n `shiftR` 16) .&amp;. 255) . (' ' :) . shows ((n `shiftR` 8) .&amp;. 255) . (' ' :) . shows (n .&amp;. 255) $ showit ns showit [] = "" </code></pre> <p>to print the values brought the time to process <code>[0 .. 1048575]</code> from 0.9 seconds to 0.4 seconds. Allocation went down from 2,031,716,528 bytes to 779,086,856 bytes, but memory usage went up from 6MB to 11MB and bytes copied during GC from ~1M to ~5.5M, however, restricting the heap size <code>-M11M</code> to force earlier GC brought memory back down to 6MB and bytes copied during GC to 676,744. (ghc-7.2.2)</p>
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    1. POEfficiently print an Array to text in Haskell (bogus, sorry)
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    1. USDaniel Fischer
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    1. CO"It's far more efficient - and may well be more efficient than using an intermediate ByteString - to produce one long String which is printed to the handle at once." This came to mind, but I had difficulty trying to make one obviously efficient string (without distressing calls to `concat` or `(++)`). I'm not good at reading Core or profiling output to know for sure. I had hope that `hPutStr` would do some buffering equivalent to lazy `String` generation (since I'm not calling `hFlush` or printing newlines). Attempts to define and print a single `String` or `ByteString` were as slow.
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      1. USmisterbee
 

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