Re: [Haskell-cafe] Mapping over Type Level Literals

11 Sep 2014

      If I were not using type literals then I would do something like this but then errors would occur at runtime.
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haarEtouffe :: Int -> Int -> Double -> Double
haarEtouffe n k t
  | n <= 0               = error "n must be >= 1"
  | k `mod`2 == 0        = error "k must be odd"
  | k < 0 || k > 2^n - 1 = error "k must be >=0 and <= 2^n -1"
  | (k' - 1) * 2 ** (-n') < t && t <= k'       * 2 ** (-n') =  2 ** ((n' - 1) / 2)
  | k'       * 2 ** (-n') < t && t <= (k' + 1) * 2 ** (-n') = -2 ** ((n' - 1) / 2)
  | otherwise                                               =  0
  where
    k' = fromIntegral k
    n' = fromIntegral n
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n :: Int
n = 100
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xss :: [[(Double, Double)]]
xss = map (\(m, k) -> map (\i -> let x = fromIntegral i / fromIntegral n in (x, haarEtouffe m k x)) [0..n - 1]) [(1,1), (2,1), (2,3), (3,1), (3,3), (3,5), (3,7)]
Dominic Steinitz
dominic@steinitz.org
http://idontgetoutmuch.wordpress.com

On 11 Sep 2014, at 21:43, Richard Eisenberg  wrote:
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On Sep 11, 2014, at 8:58 AM, Dominic Steinitz  wrote:
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But now of course I would like to map over n and k but these are at the type level. Can this be done? I imagine unsafeCoerce would have to come into it somewhere.
Mapping at the type level is probably possible, but I don't see exactly what you mean -- there aren't any lists around to map with. If you make the example a little more concrete, I may be able to help.
Richard