Definitions

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‘Definitions 

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is of ‏بح‎ ‎type Definitions associate a nam with a value of a certain ty] answer :: Int answer = 12+13 newline :: Char newline = ‘\n’ yes Bool yes = True greater :: Bool greater = (answer > 56) 

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Expressions and evaluation 

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Evaluating expressions To begin with, we have to start the Hugs interpreter; the way to do this is by using the command hugs, which produces a startup han ner lsometh 1۳۵۲0۲۲6۷۲۱30 )1(۰ 100-00 (ها اس اما الحا مايه ساديدا ‎f =I Lj ae‏ ‎Il Report bap to! huebane@kehel.ory,‏ 9 امه تسود || | موی ای و 0 تون سا اج موی لت تنعل 96 ماما ‎(Reactor Pile "/ Ware /ib/Pretrde.bs":‏ يونا مه ‎Was‏ Mawel! Prekrde be ‘Dupe 2? Por key یب یسوط مس سا و سپ پوس ‎bs Soe‏ ایب پم ‎(Sig pte pe‏ 

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(مبم) مس 0 Prekde> suv [0.00] ss Prete? 1+ O+9+F+64+047404+9400 ‏وه‎ Prekrle> (aot ‏له || (ص‎ Gree (ee eter eters یا [0.0] مس بط ‎Preknle>‏ ]9, 6,6, 9, [ Prekrle> the OO Bibs where Phe = O:0:2ip(Dik (+) Bibs (tal Pos) [O, 4, 4, 6, 9, 9, 6, 65, G4, SF] 

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rekide> puGir "kelly, ۲ << ‏ی انم‎ kell, word Prokide> ‏ان‎ "Wels, work" Welle, wort rekde> “Well” ++") "++ "World" “Welly, world" ‏مه حطس‎ ]0.( 6080008: ‏م6‎ error ia expression (uaexpevied *)') @rekide> suc 'o! CGRROR: Pye error ‏ماو و‎ oxpressiva 1 ‏معد‎ ‏و‎ ‏عد‎ + Olek ** does ant watch | [ul] ‏.]مه حطس‎ ‏لول :03000ع)‎ vartuble "a" Prehide> 

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User Defined Functions 

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Defining functions > eS fact 33 Int 5 fact n = product [1..n] fact is of type Int t Important: Y Aname starts with a letter and is followed by a sequence of letters, digits, underscore and single quotes. Y There are some reserved words like case, do and if which can not be used as identifiers. Y Only types start with a capital letter. 

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Examples square :: Int -> Int squaren=n*n allEqual :: Int -> Int -> Int->Bool allEqual m n p = (n==m) &&(n maxi :: Int -> Int -> Int maxi mn | << =n | otherwise =m exOr :: Bool -> Bool -> Bool exOr a b =(a || b) && not(a && b) 

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Working with functions @rekxe> SQuare 5 25 @retee> allEqual 8 8 8 True ‎allEqual 8 4 8‏ مم ‎False‏ ‎@rete> Maxi 7 3 ‎2 ‏0 3 2281 یه ‎9 ‏ات ‎True‏ ‎@rette> EXOr True True False ‎@retse> EXOr True (not False) False 

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ts ‘ipt looks like what you saw on slide 16. It contains definitic nitions of functions and other values) aS well as comments. ¥ Comments are preceeded by -- or enclosed in braces: -- this is a comment Arfotthis alse a comment -} fact :: Int -> Int fact n jn== =1 |n>0 =fact (n-1)*n jotherwise =0 comb :: Integer -> Integer -> Integer comb nr = fact n ‘div’ (fact r * fact (n - r)) ane number of different ways 90 electing r objects from a collection of n objects using the f ormula n!/ 0 -r)!) 

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۲۷0 5 -- myFirst.hs -- Haskell is fun -- function to raise an integer to the power of 2. squ::Int -> Int squ n = n*¥ n Literate Style FirstLit.lhs Haskell is fun function to raise an integer to the power of 2. >squ:: Int -> Int >squ n=n*n 

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‎with Scripts‏ ای ‎An expression entered at the prompt may not be longer than a line. ‎7” You can not define functions at the “prelude>” prompt. ‎” To work with a script you have to use an editor. ‎Y You have to put your scripts into files and load them when you want to use them. ‎Y You may use editors like Notepad or Wordpad to create the file and edit it. ‎Steps to follow ‎i. Open an existing file or create one using an editor ‎ii. Save the file (use only -hs or .Ihs extensions depending the on the style) ‎iii. Launch Hugs ‎iv. Load (reload ) the file you have saved ‎v. Test your functions ‎vi. edit the file to correct any errors ‎xni Save the aditted file and reneat from ctean iv 

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Getting help from Hugs 

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Summary We have learned how to "Define functions =Construct expressions using the functions we define and built-in functions "Evaluate expressions (similar to the way the numeric expressions are evaluated in a calculator.)