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81 lines
2.6 KiB
81 lines
2.6 KiB
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doubleMe x = x + x
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doubleUs x y = (doubleMe x) + (doubleMe y)
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doubleSmallNumber x = if x > 100
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then x
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else (x * 2)
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doubleSmallNumber' x = (doubleSmallNumber x) + 1
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listConcatNums = [1,2,3,4] ++ [9,10,11,12]
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-- Strings are lists of chars
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listConcatChars = "hello" ++ " " ++ "world"
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-- Cons prepends a value to a list:
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listPrependNum xs = 5:xs
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listPrependA xs = 'A':xs
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-- Access item at list index:
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listFirstValue xs = xs !! 0
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-- head, tail, last, init are useful built-ins for list operations
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-- head - get first element
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-- tail - get everything except first element
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-- last - get last element
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-- init - get everything except last element
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-- length - get length of list
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-- null - check if list is empty
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-- reverse - reverses a list
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-- take - get the first n elements of a list, if possible
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-- drop - drop the first n elements of a list, if possible
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-- maximum - get largest element in list
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-- minimum - get smallest element in list
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-- sum - add up all numbers in list
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-- product - product of all numbers in list
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-- elem - check if an item appears in a list: 4 `elem` [3,4,5,6] == True
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-- Texas ranges:
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getRangeThru n = [1..n]
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-- getRangeThru 4 == [1,2,3,4]
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getEvensThru n = [2,4..n]
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-- getEvensThru 8 == [2,4,6,8]
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-- Can use infinite ranges. e.g., get first 10 multiples of 13:
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first10of13 = take 10 [13,26,..]
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-- cycle - cycles a list infinitely - e.g. cycle [1,2,3] == [1,2,3,1,2,3,..]
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-- repeat - takes an element and produces an infinite list - e.g. repeat 5 == [5,5..]
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-- replicate - get a list of some item n times - e.g. replicate 3 10 == [10,10,10]
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-- List comprehension, like set comprehension in math:
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first10Evens = [x*2 | x <- [1..10]] -- == [2,4,6,8,10,12,14,16,18,20]
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-- We can constrain x further using predicates:
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first10EvensWhoseDoublesAreGreaterThan12 = [x*2 | x <- [1..10], x*2 >= 12] -- == [12,14,16,18,20]
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-- Say, e.g., we want to filter a list for odd numbers only, replacing those less than 10 with BOOM, else BANG
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boomBangs xs = [ if x < 10 then "BOOM!" else "BANG!" | x <- xs, odd x ]
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-- Can have multiple predicates, and multiple domains:
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multiRange = [ x*y | x <- [1..3], y <- [2..4] ] -- result will have length 9
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-- Since strings are lists, we can use list comprehension to work on them, e.g.
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removeNonUppercase st = [ c | c <- st, c `elem` ['A'..'Z']]
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-- Tuples
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-- fst - get the first item in a 2-tuple
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-- snd - get the second item in a 2-tuple
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-- zip - create pairs from 2 lists:
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zipTest1 = zip [1..3] ["one", "two", "three"] -- == [(1,"one"),(2,"two"),(3,"three")]
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-- zip clips to the shortest list:
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zipTest2 = zip [1..] ["one", "two"] -- == [(1,"one"),(2,"two")]
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