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== Usage of lists ==
Find out the results of the following operations:

<syntaxhighlight lang="Haskell">
[3,2,1] > [2,1,0]
[3,2,1] > [2,10,100]
[3,4,2] > [3,4]
[3,4,2] > [2,4]
[3,4,2] == [3,4,2]
</syntaxhighlight>

== Simple functions working with list ==
Implement following functions:
* Create a function that computes length of a list.

<syntaxhighlight lang="Haskell">length' :: [a] -> Int</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> length' "ABCD"
4
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
length' :: [a] -> Int
length' [] = 0
length' (_:xs) = 1 + length' xs
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

* Create a function that sums the list of integers.

<div style="float: right"> [[File:Video logo.png|80px|link=https://youtu.be/Yuz8lpKZiJs]]</div>
<syntaxhighlight lang="Haskell">sumIt :: [Int] -> Int</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> sumIt [1,2,3]
6
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
sumIt :: [Int] -> Int
sumIt [] = 0
sumIt (x:xs) = x + sumIt xs
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

* Create a function that returns the first element in the list.

<syntaxhighlight lang="Haskell">getHead :: [a] -> a</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> getHead [1,2,3]
1
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
getHead :: [a] -> a
getHead (x:_) = x
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

* Create a function that returns the last element in the list.

<div style="float: right"> [[File:Video logo.png|80px|link=https://youtu.be/I5AZu8_G8pQ]]</div>
<syntaxhighlight lang="Haskell">getLast :: [a] -> a</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> getLast [1,2,3]
3
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
getLast :: [a] -> a
getLast [x] = x
getLast (x:xs) = getLast xs

getLast' :: [a] -> a
getLast' (x:xs) | length xs == 0 = x
| otherwise = getLast' xs
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

* Create a function that checks if an element is a member of the list.

<syntaxhighlight lang="Haskell">isElement :: Eq a => a -> [a] -> Bool</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> isElement 2 [1,2,3]
True
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
isElement :: Eq a => a -> [a] -> Bool
isElement _ [] = False
isElement a (x:xs) | a == x = True
| otherwise = isElement a xs
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

* Create a function that returns the list without the first element.

<syntaxhighlight lang="Haskell">getTail :: [a] -> [a]</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> getTail [1,2,3]
[2,3]
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
getTail :: [a] -> [a]
getTail (_:xs) = xs
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

* Create a function that returns the list without the last element.

<div style="float: right"> [[File:Video logo.png|80px|link=https://youtu.be/ZLmvYTZ6fkw]]</div>
<syntaxhighlight lang="Haskell">getInit :: [a] -> [a]</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> getInit [1,2,3]
[1,2]
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
getInit :: [a] -> [a]
getInit [_] = []
getInit (x:xs) = x : getInit xs
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

* Create a function that merge two lists into one list.

<div style="float: right"> [[File:Video logo.png|80px|link=https://youtu.be/FFoHC-g3f_g]]</div>
<syntaxhighlight lang="Haskell">combine :: [a] -> [a] -> [a]</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> combine [1,2,3] [4,5]
[1,2,3,4,5]
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
combine :: [a] -> [a] -> [a]
combine [] y = y
combine (x:xs) y = x : combine xs y
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

* Create a function that finds the maximum in the list of integers.

<div style="float: right"> [[File:Video logo.png|80px|link=https://youtu.be/ybgM-YeQTco]]</div>
<syntaxhighlight lang="Haskell">max' :: [Int] -> Int</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> max' [3,1,7,5]
7
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
max' :: [Int] -> Int
max' [x] = x
max' (x:y:z) | x > y = max' (x:z)
| otherwise = max' (y:z)

max'' :: [Int] -> Int
max'' (y:ys) = tmp y ys where
tmp a [] = a
tmp a (x:xs) | x > a = tmp x xs
|otherwise = tmp a xs
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

* Create a function that reverse a list.

<div style="float: right"> [[File:Video logo.png|80px|link=https://youtu.be/jlUuZ5fCFgQ]]</div>
<syntaxhighlight lang="Haskell">reverse' :: [a] -> [a]</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> reverse' [3,1,7,5]
[5,7,1,3]
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
reverse' :: [a] -> [a]
reverse' [] = []
reverse' (x:xs) = (reverse' xs) ++ [x]

reverse'' :: [a] -> [a]
reverse'' n = tmp n []
where tmp [] ys = ys
tmp (x:xs) ys = tmp xs (x:ys)
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

* Create a function that product scalar multiplication if two vectors.

<syntaxhighlight lang="Haskell">scalar :: [Int] -> [Int] -> Int</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> scalar [1,2,3] [4,5,6]
32
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
scalar :: [Int] -> [Int] -> Int
scalar [] [] = 0
scalar (x:xs) (y:ys) = x*y + scalar xs ys
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/BEBLH60352]]
</div>
<div style="clear:both"></div>

@@ Line 274: / Line 274: @@
 * Create a function that compares lists of numbers if they are equal.
-<syntaxhighlight lang="Haskell">compareLists :: [a] -> [a] -> Bool </syntaxhighlight>
+<syntaxhighlight lang="Haskell">compareLists :: Eq a => [a] -> [a] -> Bool </syntaxhighlight>
 <syntaxhighlight lang="Haskell" class="myDark">
 *Main> compareLists [5,8,11] [5,8,11]

@@ Line 213: / Line 213: @@
 <div style="clear:both"></div>
-* Create a function that product scalar multiplication if two vectors.
+* Create a function that product scalar multiplication of two vectors.
 <syntaxhighlight lang="Haskell">scalar :: [Int] -> [Int] -> Int</syntaxhighlight>
@@ Line 230: / Line 230: @@
 </div>
 <div style="clear:both"></div>

FP Laboratory 3/en - Revision history

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