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I need to implement a split function in haskell where user gives the as a example input

splitx [1,2,3,4,5,6] 3

should output -> [1,2,3]

splitx::[Int]->Int->[Int]
splitx [] 0 = []
splitx (x:xs) n = x: splitx xs (n-1)

i wrote the following function but it gives a error 

Non-exhaustive patterns in function Main.splitx

just tell me where am i wrong ?

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  • does you function return the first n elements? is that a requirement? Commented Jul 9, 2011 at 8:13

4 Answers 4

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What should splitx [] n be? And how does the computer know that?

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good point.. well, with the current code it is undefined, which matches the specification :)
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If you want to return the first n elements:

you have no pattern match for input where n=0 and list is not empty:

splitx _ 0 = []

Note: specify the type to be generic so it works not only with Ints:

splitx :: [a] -> Int -> [a]
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4 Comments

yet its returns be the full list :-o
While your solution is correct, the explanation is not! The only missing pattern is splitx [] n where n is not equal to zero. The pattern splitx _ 0 is matched by splitx (x:xs) n.
You are right. What I wanted to say is that it's matched but shouldn't be, because you want to terminate at that point.
@Rotsor @yi_H thanks for the answers . my problem is always i only consider about the main pattern matching thiggy :-s
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The error (actually warning, i believe) that you are receiving is complaining that the pattern matches (on the left side of the =) are not exhaustive. You need to add an extra case for the situation where you get [] and n as arguments.

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By following this suggestion one will get a specialisation of const :)
Derp, I was going on 36 hours without sleep when I wrote my original answer. I've corrected my answer by removing my code examples.
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Now that your original question is answered, do you have to use recursion and pattern matching for your homework? If not, you'll notice that splitx is a lot like take with reversed arguments:

GOA> let splitx = flip take
GOA> splitx [1,2,3,4,5,6] 3
[1,2,3]
GOA> splitx [1,2,3,4,5,6] 0
[]
GOA> splitx [] 3
[]
GOA> splitx "abcde" 3
"abc"
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