GitHub - Violent-Profession-Transition/Haskell_Reborn: Haskell, the cure for depression

想像力こそが、すべてを変える。

学習リソース:

Notes with Paul-ZQ Jan 19th @NUS-ALSET:

Haskell disallows multiple declaration of variable during a program's runtime. So in GHCi, you can assign different values to a variable name multiple times, but in a .hs program, the variable is tied to an expression/value.
A variable in Haskell is a name that is bound to the expression/value on the right, unlike in imperative programming's memory location abstraction.
Haskell does not have a return keyword, because a function is a single expression, not a sequence of statements. The value of the expression is the result of the function, and a function can be evaluated to be another partial function like partialMod = mod x.
In imperative language, we can just write if without providing a branch for else. In Haskell, because we work with expression, an if that does not have else branch will not evaluate to a value if the predicate is False.

-- Haskell must provide an evaluated result for all branches
ifFunc x = if (x>10) then "Big number" else "Small number"
-- ifFunc 11 -> "Big number"

Haskell is lazy, take 3 [1,2..] will be [1,2,3]
: operator takes in an item and return -> a function that takes in a list and -> return a list.

*Main> :t (:)
(:) :: a -> [a] -> [a]
*Main> (:) 1 [1]
[1,1]

Pattern matching involving () and []. Since :'s second input is a list type, so (x:xs) actually means some x concats to a list xs.

someFunc :: [Char] -> Char
someFunc [] = '1'
someFunc (x:[]) = x
someFunc (x:xs) = head xs

-- in GHCi
*Main> someFunc "dettol"
'e'

Name		Name	Last commit message	Last commit date
Latest commit History 18 Commits
README.md		README.md
Week_1_Baby_Functions.hs		Week_1_Baby_Functions.hs
Week_1_Lists.hs		Week_1_Lists.hs
Week_1_One_hour_Haskell_Derek.hs		Week_1_One_hour_Haskell_Derek.hs
Week_1_Tuple.hs		Week_1_Tuple.hs
Week_1_Types_TypeClasses.hs		Week_1_Types_TypeClasses.hs
Week_2_Function_Syntax.hs		Week_2_Function_Syntax.hs
Week_3_Defining_Types.hs		Week_3_Defining_Types.hs
Week_3_Higher_Order_Functions.hs		Week_3_Higher_Order_Functions.hs
Week_3_Lambdas_Folds.hs		Week_3_Lambdas_Folds.hs
Week_3_Modules.hs		Week_3_Modules.hs
Week_3_Recursion.hs		Week_3_Recursion.hs
Week_4_CIS194_Intro.hs		Week_4_CIS194_Intro.hs
Week_4_CIS194_Intro_Homework1.hs		Week_4_CIS194_Intro_Homework1.hs
Week_7_FiveThingsAboutHaskellTalk_GeekCamp2019Jan05.hs		Week_7_FiveThingsAboutHaskellTalk_GeekCamp2019Jan05.hs
Week_7_TypeOfAndTypeSymbols.hs		Week_7_TypeOfAndTypeSymbols.hs
Week_8_Currying_LYAH.hs		Week_8_Currying_LYAH.hs
Week_9_IntroSession.hs		Week_9_IntroSession.hs

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