[Haskell-cafe] Clarification Please

PR Stanley prstanley at ntlworld.com
Thu Sep 13 23:10:39 EDT 2007


I'm not sure. We start with one list and also, 
perhaps I should have mentioned that I have a 
merge function which takes two sorted lists with 
similar, now, what do they call it, similar 
orientation? and merges them into one sorted list.
e.g. merge [1, 4,] [2, 3]
[1,2,3,4]
Cheers, Paul
At 04:02 14/09/2007, you wrote:
>Define a merge function that merges two sorted 
>lists into a sorted list containing all the 
>elements of the two lists.  Then define the 
>msort function, which will be recursive.
>
>Mike
>
>PR Stanley wrote:
>>Hi
>>Taken from chapter 6, section 8 of the Hutton book on programming in Haskell:
>>5. Using merge, define a recursive function
>>msort :: (Ord a) => [a] -> [a]
>>that implements merge sort, in which the empty 
>>list and singleton lists are already sorted, 
>>and any other list is sorted by merging 
>>together the two lists that result from sorting 
>>the two halves of the list separately. :
>>Hint: first define a function
>>¬halve :: [a] -> [([a], [a])]
>>¬that splits a list into two halves whose length differs by at most one.
>>     Create a halve function - okay, that's 
>> fairly straightforward. The rest, I'm afraid, 
>> is a little obscure. I'm not looking for the 
>> solution; I'd like to work that out for 
>> meself. However, I'd  really appreciate some 
>> clues as to the general structure of the algorithm.
>>Much obliged,
>>Paul
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