9

PureScript Cheat Sheet For JavaScript Developers

 3 years ago
source link: https://blog.oyanglul.us/purescript/cheatsheet
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
PureScript Cheat Sheet For JavaScript Developers

PureScript Cheat Sheet For JavaScript Developers

Table of Contents

Literal

Number

let a = 1
let b = 1.2

PureScript

a :: Int
a = 1
b :: Number
b = 1.2

String

let a = "yay"
let multiline = `first line
second line
third line`
let concatString = "a" + "b"

PureScript

a :: String
a = "yay"
multiline = """first line
second line
third line"""
concatString = "a" <> "b"

Boolean

let a = true
let b = false

PureScript

a :: Boolean
a = true

b :: Boolean
b = false

Records

let a = {key1: "value1", key2: true}

let b = Object.assign({}, a, {key1: "new value1"})

function updateKey2To(record) {
  return (value) => Object.assign({}, record, {key2: value})
}

PureScript

a :: {key1:: String, key2:: Boolean}
a = {key1: "value1", key2: true}

b = a {key1 = "new value1"}

updateKey2To = _ {key2 = _}

Function

function sum(x, y) { return x + y }
let lambdaSum = (x, y) => (x + y)

function fib(n) {
  if(n == 0) return 1
  else if(n == 1) return 1
  else return fib(n-1) + fib(n-2)
}

PureScript

sum :: Int -> Int -> Int
sum x y = x + y

lambdaSum :: Int -> Int -> Int
lambdaSum = \x y -> x + y

fib :: Int -> Int
fib 0 = 1
fib 1 = 1
fib n = fib (n-1) + fib (n-2)

Control Flow

If-Else

let tof = true ? true : false

PureScript

tof :: Boolean
tof = if true then true else false

Scope

let a = 1
function inScope() {
  let a = 2
  return a
}

PureScript

a = 1
inScope = a
  where a = 2
-- or
inScope = let a = 2
  in a

Pattern Matching

JS ES proposal

let res = {status: 404}
let entity = case (res) {
  when {status: 200, body: b} ->
    b
  when {status: s} ->
    throw "error" + s
}

PureScript

res :: {status:: Int, body:: String}
res = {status: 404, body: ""}

entity = case res of
  {status: 200, body: b} -> Right b
  e -> Left $ show e

Do Notaion / FlatMap

JavaScript(ES2019) has flatMap for Array 

let a = [1,2,3]
let b = [2,3,4]
let c = a.flatMap(x=> b.flatMap(y => x+y))

PureScript

flatMap in PureScript is the same as Haskell >>= 

a = [1,2,3]
b = [2,3,4]
c = a >>= \x -> (b >>= \y -> x + y)

and you can use do notation for nicer syntax 

a = [1,2,3]
b = [2,3,4]
c = do
  x <- a
  y <- b
  pure x + y

not only Array, you can flatMap on any kind that has Monad instance i.e. Maybe

Modules

JavaScript modules are based on file directory 

// import module from somefile.js
import {method} from './some-file'
// export module
const a = 1
export a

PureScript

While PureScript is namespace based 

-- file ramdom-file-name.purs
module A where
a = 1

so just module name matter, the file name doesnot matter 

module B where
import A
-- not import './ramdom-file-name'

report

Recommend

About Joyk


Aggregate valuable and interesting links.
Joyk means Joy of geeK