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Haskell 勉強記録 10 日目

Haskell 勉強記録

すごいHaskellたのしく学ぼう!

すごいHaskellたのしく学ぼう!

今日は 第6章:モジュール キーから値へのマッピング (位置 2545/11175) まで読み進めました。

読み進むうちに、だんだん疑問が増えてきました。

  • Just は大文字で始まるので普通の関数じゃないんだろけどでは何だろう?
  • any という関数は Data.List モジュールにも Prelude にもあるけど同じものなのか
  • 上を確かめたくて、関数が同一であるかを調べようとしたけれど、どうやって調べれば良いのか。(他の言語みたいに (List.any) == (any) とは出来ない)

今まで出てた関数

-- Prelude 
5 + 2                  == 8
5 * 2                  == 10
5 - 2                  == 3
5 / 2                  == 2.5
( True || False )      == True
( True && False )      == False
not True               == False
succ 'c'               == 'd'
min 4 5                == 4
max 'a' 'z'            == 'z'
div 92 3               == 30
mod 14 5               == 4
[1,2,3] ++ [4,5]       == [1,2,3,4,5]
'a':" long time"       == "a long time"  
"abcdef" !! 2          == 'c'
( [1,2,3] < [1,2,4] )  == True
( "bbc" > "abc" )      == True
( [1,2,3] <= [1,2,4] ) == True
( "bbc" >= "abc" )     == True
( "abc" == "abc" )     == True
(1.0 /= 1.5)           == True 
head [1..]             == 1
tail [1,2,3]           == [2,3]
init [1,2,3,4]         == [1,2,3]
length ['a'..'z']      == 26
null []                == True
reverse [1,2,3]        == [3,2,1]
take 3 [1..]           == [1,2,3]
drop 7 [1..10]         == [8,9,10]
maximum [1,10,2]       == 10
minimum [3,2,4]        == 2
sum [1,10,100]         == 10
product [2,3,4]        == 24
elem 4 [1,2,3,4,5]     == True
take 10 ( cycle "abc") == "abcabcabca"
take 5 ( repeat 'x')   == "xxxxx"
replicate 5 'x'        == "xxxxx"
odd 5                  == True
even 8                 == True
fst (1,'A')            == 1
snd (1,'A')            == 'A'
zip [1..] "ABC"        == [(1,'A'),(2,'B'),(3,'C')]
show 4.25              == "4.25"
(read "4" :: Int)      == 4 
(minBound :: (Bool, Int, Char))  == (False,-9223372036854775808,'\NUL') 
(maxBound :: (Bool, Int, Char))  == (True,9223372036854775807,'\1114111')
fromIntegral (div 5 3) + 1.5     == 2.5 
compare 1 2                      == LT
zipWith (*) [1..3] [10,20,30]    == [10,40,90]
flip (++) "DEF" "ABC"            == "ABCDEF"
map (10-) [1..3]           == [9,8,7]
filter (<3) [1..10]        == [1,2]
takeWhile (/= 'd') "abracadabra" == "abraca"
foldl (-) 10 [1,2]         == 7
foldr (-) 10 [1,2]         == 9
foldl1 (-) [10,1,2]        == 7
foldr1 (-) [1,2,10]        == 9
and [True, False, True]    == False
or  [True, False, True]    == True
scanl (+) 0 [1,2,3]        == [0,1,3,6]
scanr (+) 0 [1,2,3]        == [6,5,3,0]
scanl1 (+) [1,2,3]         == [1,3,6]
scanr1 (+) [1,2,3]         == [6,5,3]
abs (-9)                   == 9
sqrt 9                     == 3.0
negate 3.0                 == -3.0
negate $ sqrt $ abs (-9)   == -3.0
(negate . sqrt . abs) (-9) == -3.0

-- import qualified Data.List as List
List.nub "abracadabra"          == "abrcd"
List.sort [9,8..0]              == [0,1,2,3,4,5,6,7,8,9]
List.words "I don't like it!"   == ["I","don't","like","it!"]
List.group "aaabbcca"           == ["aaa","bb","cc","a"]
List.tails [1,2,3]              == [[1,2,3],[2,3],[3],[]]
List.isPrefixOf "Hi" "Hiroshi!" == True
List.any (== 'c') "abcdef"      == True
List.isInfixOf "abc" "xxabcyy"  == True 
List.foldl'                     -- foldl の正格(Strict evaluation)版
List.foldr'                     -- foldr の正格(Strict evaluation)版
List.find (== 0) [1,2,3]        == Nothing

-- import qualified Data.Char as Char
Char.ord 'A'                    == 65
Char.chr 97                     == 'a'
Char.digitToInt '2'             == 2

-- import qualified Data.Map as Map
Map.fromList [(1,"One"), (2,"Two")]    == fromList [(1,"One"),(2,"Two")]
Map.lookup 2 $ Map.fromList [(1,"A"), (2,"B")] == Just "B"
Map.fromListWith (+) [("A",1),("B",2),("A",3)] == fromList [("A",4),("B",2)]