Hector, That line is declaring a function named 'f' of two arguments: one is 'w', and the other is a tuple. The tuple's fst is 'inputs', and its snd is 'expected.' This function (f) is used in the next line, in the declaration of the list 'newWeights,' which uses f as the function which does the fold over the allInputs list.
Cheers, - Tim On Thu, Oct 29, 2009 at 2:27 PM, Hector Guilarte <hector...@gmail.com>wrote: > Hi cafe, > > I'm trying to implement a Perceptron in Haskell and I found one in: > http://jpmoresmau.blogspot.com/2007/05/perceptron-in-haskell.html (Thanks > JP Moresmau) but there is one line I don't understand, I was wondering if > someone could explain it to me. I know the theory behind a perceptron, my > question is more about the Haskell syntax in that line I don't understand. > > epoch :: [([Float],Float)] -> -- ^ Test Cases and Expected Values for each > test case > [Float] -> -- ^ weights > ([Float],Float) -- ^ New weights, delta > epoch allInputs weights= > let > f w (inputs,expected) = step inputs w expected -- I don't > understand this line > newWeights = foldl f weights allInputs -- Neither this one > delta = (foldl (+) 0 (map abs (zipWith (-) newWeights weights))) / > (fromIntegral $ length weights) > in (newWeights,delta) > > What is f and what is w? I really don't get it, Is like it is defining a > function f which calls step unziping the input, taking one of the elements > from the fst and it's corresponding snd and invoking step with that, along > with w (which seems to be a list according to step's signature but I don't > know where it comes from), and then applying fold to the weights and all the > Inputs using that f function... But I don't get it! > > Maybe if someone could rewrite that redefining f as an separate function > and calling fold with that function I'll get it. > > The input for epoch would be something like this: > epoch [([0,0],0),([0,1],0),([1,0],0),([1,1],1)] [-0,413,0.135] > > and the output for that examples is: > ([0.0,412.9],3.333537e-2) > > > Thanks a lot, > > Hector Guilarte > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >
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