<div dir="auto"><div>GHC has deduced that the third and fourth arguments of stdDev must be members of both the Floating and Integral classes based on the functions used on them. GHC has also deduced that the types of y and x are [Float] and [[Float]] respectively. The error is that GHC has no definition in scope that would make Float a member of the Integral class. </div><div dir="auto"><br></div><div dir="auto">How to fix this is a bit more than I can go into right now, but will likely involve carefully converting from type to type at particular points in stdDev. As a first step, it's always a good idea to explicitly tell GHC what YOU think the types are for a function, and then let it tell you where it disagrees.<br><br><div class="gmail_quote" dir="auto"><div dir="ltr">On Thu, Aug 23, 2018, 6:26 AM Jack Vice <<a href="mailto:jack.vice@gmail.com">jack.vice@gmail.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><p style="margin:0px 0px 1em;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:Arial,"Helvetica Neue",Helvetica,sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(36,39,41)">I am trying to calculate the standard deviation for each index in a list of lists of floats. Using Ubuntu 18.04, ghc 8.0.2. I am getting the following runtime error which I have googled and still don't understand what "Integral Float" is exactly or even which parameter is causing the trouble.</p><pre style="margin-top:0px;margin-bottom:1em;padding:5px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:Consolas,Menlo,Monaco,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",monospace,sans-serif;font-size:13px;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;background-color:rgb(239,240,241);word-wrap:normal;color:rgb(36,39,41)"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:Consolas,Menlo,Monaco,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",monospace,sans-serif;vertical-align:baseline;box-sizing:inherit;white-space:inherit">*Main> let z = stdDev 0 2 y x
<interactive>:250:9: error:
• Could not deduce (Integral Float) arising from a use of ‘stdDev’
  from the context: Floating a
    bound by the inferred type of z :: Floating a => [a]
    at <interactive>:250:5-38
• In the expression: stdDev 0 (length (head (x))) y x
  In an equation for ‘z’: z = stdDev 0 (length (head (x))) y x
</code></pre><p style="margin:0px 0px 1em;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:Arial,"Helvetica Neue",Helvetica,sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(36,39,41)">Code:</p><pre style="margin-top:0px;margin-bottom:1em;padding:5px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:Consolas,Menlo,Monaco,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",monospace,sans-serif;font-size:13px;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;background-color:rgb(239,240,241);word-wrap:normal;color:rgb(36,39,41)"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:Consolas,Menlo,Monaco,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",monospace,sans-serif;vertical-align:baseline;box-sizing:inherit;white-space:inherit">-- i is start index, l is length of each list, ms is list of means, 
--    xs is Matrix
stdDev i l ms xs
     | i < l     = sqrt(fromIntegral(sumOfMinusMeans i (ms!!i) xs) / 
                             fromIntegral(l)):(stdDev (i+1) l ms xs)
     | otherwise = []

--i is index, m is mean for the index
sumOfMinusMeans i m (x:xs)
     | xs == []     = (x!!i - m)**2
     | i < length x = (x!!i - m)**2 + (sumOfMinusMeans i m xs)
     | otherwise    = 0
</code></pre><p style="margin:0px 0px 1em;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:Arial,"Helvetica Neue",Helvetica,sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(36,39,41)">Types:</p><pre style="margin-top:0px;margin-bottom:1em;padding:5px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:Consolas,Menlo,Monaco,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",monospace,sans-serif;font-size:13px;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;background-color:rgb(239,240,241);word-wrap:normal;color:rgb(36,39,41)"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:Consolas,Menlo,Monaco,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",monospace,sans-serif;vertical-align:baseline;box-sizing:inherit;white-space:inherit">*Main> :t stdDev
stdDev
  :: (Floating a1, Floating a, Integral a1) =>
     Int -> Int -> [a1] -> [[a1]] -> [a]

*Main> :t sumOfMinusMeans
sumOfMinusMeans :: (Eq t, Floating t) => Int -> t -> [[t]] -> t
</code></pre><p style="margin:0px 0px 1em;padding:0px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:Arial,"Helvetica Neue",Helvetica,sans-serif;font-size:15px;vertical-align:baseline;box-sizing:inherit;clear:both;color:rgb(36,39,41)">Variables:</p><pre style="margin-top:0px;margin-bottom:1em;padding:5px;border:0px;font-variant-numeric:inherit;font-variant-east-asian:inherit;font-stretch:inherit;line-height:inherit;font-family:Consolas,Menlo,Monaco,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",monospace,sans-serif;font-size:13px;vertical-align:baseline;box-sizing:inherit;width:auto;max-height:600px;overflow:auto;background-color:rgb(239,240,241);word-wrap:normal;color:rgb(36,39,41)"><code style="margin:0px;padding:0px;border:0px;font-style:inherit;font-variant:inherit;font-weight:inherit;font-stretch:inherit;line-height:inherit;font-family:Consolas,Menlo,Monaco,"Lucida Console","Liberation Mono","DejaVu Sans Mono","Bitstream Vera Sans Mono","Courier New",monospace,sans-serif;vertical-align:baseline;box-sizing:inherit;white-space:inherit">*Main> y
[380.0,1.0]
*Main> x
[[600.0,1.0],[400.0,1.0],[170.0,1.0],[430.0,1.0],[300.0,1.0]]</code></pre></div>
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