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I'm just beginning this nice hashkell beginners tutorial:
http://learnyouahaskell.com
on this page on lists he explains that lists are compared in compared in lexicographical order, he gives this example:
ghci> [3,2,1] > [2,10,100] True From some googling it seems to me that lexicographical ordering means in alphabetical or sequential number ordering(?), but I still can't make sense of this evaluating to True.
I'm missing something obvious here, can anybody help?
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In mathematics, the lexicographic or lexicographical order (also known as lexical order, or dictionary order) is a generalization of the alphabetical order of the dictionaries to sequences of ordered symbols or, more generally, of elements of a totally ordered set.
Defining Lexicographical Order Thus, lexicographical order is a way for formalizing word order where the order of the underlying symbols is given. In programming, lexicographical order is popularly known as Dictionary order and is used to sort a string array, compare two strings, or sorting array elements.
When applied to numbers, lexicographic order is increasing numerical order, i.e. increasing numerical order (numbers read left to right). For example, the permutations of {1,2,3} in lexicographic order are 123, 132, 213, 231, 312, and 321. When applied to subsets, two subsets are ordered by their smallest elements.
This evaluates to True as 3 is greater than 2. Having found a result, the comparison stops here. He's demonstrating that 2 and 10 are not compared. The result of the array comparison is true. If the first array started with 2 as well, the comparison would result in false.
A nice example for when lexicographical ordering does not result in what the user would expect is file names in Windows. If you have files named xyz1.txt, xyz2.txt, xyz10.txt and xyz20.txt, the lexicographical order would be: xyz1.txt, xyz10.txt, xyz2.txt, xyz20.txt
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