setup the compiler and REPL

brew install ghc

It comes with 2 programs:

1. ghc: (Glasgow Haskell Compiler)
2. ghci: REPL (Read-Eval-Print Loop) for Haskell

Just run ghci in the terminal to start the REPL.

To quit the REPL, type :quit or :q. (But I just do ctrl + d, haha)

To write multiple line code in the REPL, use :{ and :}.

:{
add :: Int -> Int -> Int
add x y = x + y
:}

setup ghcup

The offical haskell recommend using GHCup as installer.

My experience installing ghcup is not that smooth:

1. the doc recommend using curl --proto '=https' --tlsv1.2 -sSf https://get-ghcup.haskell.org | sh for downloading the install shell script and running it. Somehow it didn't work for me, after removing the --tlsv1.2 part, it worked.
2. you may need to manually append the path(usually ~/.ghcup/bin) to the PATH variable in your shell profile file.

try out ghci

-- this is a comment, no `;` at the end
print "Hello, World!"
-- declare var
greeting = "Hello, World!"
print greeting
-- get user input
print "What's your name"
name <- getLine
print "Hello " ++ name

• operators

True && False
False || True

1 == 2
1 /= 2 -- not equal

2 > 1
1 <= 2

2 - 1
2 + 1
2 * 3
5 / 2 -- 2.5
6 / 2 -- 3.0

mod 5 2
div 5 2 -- 2

2 ^ 3

ceiling 3.4
floor 3.4
round 3.4
round 3.5

max 2 4
min 2 4

• add

-- func is just a var, no special identifier, man I like it!
add :: Int -> Int -> Int -- type signature, optional
add x y = x + y
add 1 2 -- call the function

• partial application

increase = add 1
increase 2

write/compile code in a file

convention: haskell file extension is .hs

create a file named main.hs:

factorial :: Int -> Int
factorial 0 = 1
factorial n = n * factorial (n - 1)

sumList :: [Int] -> Int
sumList [] = 0
sumList (x:xs) = x + sumList xs

findMax :: [Int] -> Int
findMax [] = error "empty list"
findMax [x] = x
findMax (x:xs) = max x (findMax xs) -- max is a built-in function

main = do
  print (factorial 5)
  -- using $ to avoid parentheses
  print $ sumList [1, 2, 3, 4, 5]
  print $ findMax [1, 2, 3, 4, 5]

compile it:

ghc -o main main.hs

It'll generate 3 files:

1. main: executable
2. main.hi: intermediate file (like a header/declaration file?)
3. main.o: object file (for linking)

read an intro book

In Haskell's official website, there's a list of books and tutorials:

This is the book I'm reading: Learn You a Haskell for Great Good!

Learning from this book will be covered in basic-topics folder.