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== Operators ==
*Define following functions that performs corresponding logic operations: <code>not', and', or', nand', xor', impl', equ'</code>
*Define the 'standard' priority for all these functions, if they are used as operators.
*Create a function that prints the truth table of a given logical expression for two variables.

<syntaxhighlight lang="Haskell">table :: (Bool -> Bool -> Bool) -> IO ()</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
table (\a b -> (and' a (or' a b)))
True True True
True False True
False True False
False False False
</syntaxhighlight>

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<syntaxhighlight lang="Haskell">

not' :: Bool -> Bool
not' True = False
not' False = True
infixl 5 `not'`

and' :: Bool -> Bool -> Bool
and' True True = True
and' _ _ = False
infixl 4 `and'`

or' :: Bool -> Bool -> Bool
or' False False = False
or' _ _ = True
infixl 3 `or'`

nand' :: Bool -> Bool -> Bool
nand' x y = not' (and' x y)
infixl 4 `nand'`

xor' :: Bool -> Bool -> Bool
xor' x y = x/=y
infixl 3 `xor'`

impl' :: Bool -> Bool -> Bool
impl' True False = False
impl' _ _ = True
infixl 2 `impl'`

equ' :: Bool -> Bool -> Bool
equ' x y = x == y
infixl 7 `equ'`

table :: (Bool -> Bool -> Bool) -> IO ()
table expr = putStr (concat [nicePrint [x,y,(expr x y)] |x<-[True,False], y<-[True,False]])

nicePrint :: [Bool] -> String
nicePrint xs = concat [show x++"\t"| x<-xs] ++ "\n"
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/GWCM50489]]
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*Extend the previously defined function to accept any number of variables (the number of variables will be given as a first parameter).

<syntaxhighlight lang="Haskell">tablen :: Int -> ([Bool] -> Bool) -> IO ()</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
tablen 3 (\[a,b,c] -> a `and'` (b `or'` c) `equ'` a `and'` b `or'` a `and'` c)
True True True => True
True True False => True
True False True => True
True False False => False
False True True => False
False True False => False
False False True => False
False False False => False
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
tablen :: Int -> ([Bool] -> Bool) -> IO ()
tablen n f = putStr(concat [nicePrint x ++ " => " ++ show(f x) ++ "\n" |x<-allValues n]) where
allValues 1 = [[True], [False]]
allValues n = [x:y| x<-[True,False], y<-allValues (n-1)]

nicePrint :: [Bool] -> String
nicePrint xs = concat [show x++"\t"| x<-xs]
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/IDZIG48578]]
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== Complex function - Huffman Codes ==
*Create a function that will compute [https://en.wikipedia.org/wiki/Huffman_coding Huffman codes] for a given list of characters and their frequencies.

<div style="float: right"> [[File:Video logo.png|80px|link=https://youtu.be/HWYQZtbxMhc]]</div>
<syntaxhighlight lang="Haskell">huffman :: [(Char, Int)] -> [(Char, String)]</syntaxhighlight>
<syntaxhighlight lang="Haskell" class="myDark">
*Main> huffman [('a',45),('b',13),('c',12),('d',16),('e',9),('f',5)]
[('a',"0"),('b',"101"),('c',"100"),('d',"111"),('e',"1101"),('f',"1100")]
</syntaxhighlight>

<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
<syntaxhighlight lang="Haskell">
import Data.List (sortBy)

huffman :: [(Char, Int)] -> [(Char, String)]
huffman input =
let
prep = [ (y, [(x,"")] ) | (x,y)<-input]
in sortBy (\ (x,_) (y,_) -> compare x y) (step prep) where
step :: [(Int, [(Char, String)])] -> [(Char, String)]
step [(_, result) ] = result
step list = let ((a1, as2):(b1,bs2):rest) = sortBy (\ (x,_) (y,_) -> compare x y) list
in step ((a1+b1, [(x,'0':a2)|(x,a2)<-as2]++[(x,'1':b2)|(x,b2)<-bs2]) : rest)
</syntaxhighlight>
[[File:Tryit.png|center|60px|Try it!|link=https://rextester.com/PSSTZ19890]]
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@@ Line 1: / Line 1: @@
 == Operators ==
 *Define following functions that performs corresponding logic operations: <code>not', and', or', nand', xor', impl', equ'</code>
 *Define the 'standard' priority for all these functions, if they are used as operators.
@@ Line 114: / Line 114: @@
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FP Laboratory 6/en - Revision history

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