The parens around max are unnecessary:
myMax xs = foldl1 max xs
On Fri, Sep 25, 2015 at 5:13 PM
El 2015-09-25 18:57, Francesco Ariis escribió:
On Fri, Sep 25, 2015 at 06:18:08PM -0500, jamb@hinojosa.com wrote:
Hello,
I am a complete Haskell beginner and I am doing some exercises of my book but I am stuck with the following:
Define myMax :: Ord a => [a] -> a which returns the maximum element of a list.
I must use foldl1 or foldr1 and I am given the hint to use max which gets the maximum of 2 elements.
I will very much appreciate if you help me solve it.
Let's say you have
foldl1 f [1,7,2,5]
where f is a binary operator (a function that 'takes two parameters'). `foldl1` will apply 1 and 7 to f, obtaining X, so we have:
X and [2,5]
then it will apply X and 2 to f, obtaining Y, so we're left with
Y and 5
and finally `f Y 5`, leading to your final result Z.
Now, if `f a b = a + b`, we would have
[1,7,2,5] -- 1+7 8 [2,5] -- 8+2 10 [5] -- 10+5 15 <-- final result
But you aren't interested in the sum of the list, but its maximum. Which operation could you use instead of (+) to achieve your goal? _______________________________________________ Beginners mailing list Beginners@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
I´ve got it! I tried the following successfully:
myMax [] = error "List is empty." myMax xs = foldl1 (max) xs
I see that my problem was in understanding the way max was applied to a list.
Thanks for your kind support.
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