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updated purescript example for compiler version >= 0.7.4.1
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thimoteus
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language: purescript
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contributors:
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- ["Fredrik Dyrkell", "http://www.lexicallyscoped.com"]
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- ["Thimoteus", "https://github.com/Thimoteus"]
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---
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PureScript is a small strongly, statically typed language compiling to Javascript.
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* Learn more at [http://www.purescript.org/](http://www.purescript.org/)
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* Documentation: [http://docs.purescript.org/en/latest/](http://docs.purescript.org/en/latest/)
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* Documentation: [http://pursuit.purescript.org/](http://pursuit.purescript.org/)
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* Book: Purescript by Example, [https://leanpub.com/purescript/](https://leanpub.com/purescript/)
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```haskell
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```purescript
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--
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-- 1. Primitive datatypes that corresponds to their Javascript
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-- equivalents at runtime.
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> import Prelude
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-- Numbers
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1 + 7*5 :: Number -- 36
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> 1.0 + 7.2*5.5 :: Number -- 40.6
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-- Ints
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> 1 + 2*5 :: Int -- 11
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-- Types are inferred, so the following works fine
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9 / 2.5 + 4.4 -- 8
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> 9.0/2.5 + 4.4 -- 8.0
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-- But Ints and Numbers don't mix, so the following won't
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> 5/2 + 2.5 -- Expression 2.5 does not have type Int
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-- Hexadecimal literals
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0xff + 1 -- 256
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> 0xff + 1 -- 256
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-- Unary negation
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6 * -3 -- -18
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6 * negate 3 -- -18
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-- Modulus
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3 % 2 -- 1
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4 % 2 -- 0
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> 6 * -3 -- -18
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> 6 * negate 3 -- -18
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-- Modulus, from purescript-math (Math)
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> 3.0 % 2.0 -- 1.0
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> 4.0 % 2.0 -- 0.0
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-- Inspect the type of an expression in psci
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:t 9 / 2.5 + 4.4 -- Prim.Number
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> :t 9.5/2.5 + 4.4 -- Prim.Number
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-- Booleans
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true :: Boolean -- true
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false :: Boolean -- false
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> true :: Boolean -- true
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> false :: Boolean -- false
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-- Negation
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not true --false
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23 == 23 -- true
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1 /= 4 -- true
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1 >= 4 -- false
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> not true -- false
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> 23 == 23 -- true
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> 1 /= 4 -- true
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> 1 >= 4 -- false
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-- Comparisions < <= > >=
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-- are defined in terms of compare
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compare 1 2 -- LT
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compare 2 2 -- EQ
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compare 3 2 -- GT
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> compare 1 2 -- LT
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> compare 2 2 -- EQ
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> compare 3 2 -- GT
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-- Conjunction and Disjunction
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true && (9 >= 19 || 1 < 2) -- true
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> true && (9 >= 19 || 1 < 2) -- true
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-- Strings
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"Hellow" :: String -- "Hellow"
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-- Multiline string
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"Hellow\
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> "Hellow" :: String -- "Hellow"
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-- Multiline string without newlines, to run in psci use the --multi-line-mode flag
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> "Hellow\
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\orld" -- "Helloworld"
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-- Multiline string with newlines
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> """Hello
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world""" -- "Hello\nworld"
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-- Concatenate
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"such " ++ "amaze" -- "such amaze"
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> "such " ++ "amaze" -- "such amaze"
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--
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-- 2. Arrays are Javascript arrays, but must be homogeneous
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[1,1,2,3,5,8] :: [Number] -- [1,1,2,3,5,8]
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[true, true, false] :: [Boolean] -- [true,true,false]
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> [1,1,2,3,5,8] :: Array Number -- [1,1,2,3,5,8]
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> [true, true, false] :: Array Boolean -- [true,true,false]
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-- [1,2, true, "false"] won't work
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-- `Cannot unify Prim.Number with Prim.Boolean`
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-- `Cannot unify Prim.Int with Prim.Boolean`
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-- Cons (prepend)
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1 : [2,4,3] -- [1,2,4,3]
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> 1 : [2,4,3] -- [1,2,4,3]
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-- Requires purescript-arrays (Data.Array)
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-- and purescript-maybe (Data.Maybe)
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-- Safe access return Maybe a
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head [1,2,3] -- Just (1)
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tail [3,2,1] -- Just ([2,1])
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init [1,2,3] -- Just ([1,2])
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last [3,2,1] -- Just (1)
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> head [1,2,3] -- Just (1)
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> tail [3,2,1] -- Just ([2,1])
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> init [1,2,3] -- Just ([1,2])
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> last [3,2,1] -- Just (1)
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-- Random access - indexing
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[3,4,5,6,7] !! 2 -- Just (5)
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> [3,4,5,6,7] !! 2 -- Just (5)
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-- Range
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1..5 -- [1,2,3,4,5]
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length [2,2,2] -- 3
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drop 3 [5,4,3,2,1] -- [2,1]
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take 3 [5,4,3,2,1] -- [5,4,3]
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append [1,2,3] [4,5,6] -- [1,2,3,4,5,6]
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> 1..5 -- [1,2,3,4,5]
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> length [2,2,2] -- 3
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> drop 3 [5,4,3,2,1] -- [2,1]
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> take 3 [5,4,3,2,1] -- [5,4,3]
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> append [1,2,3] [4,5,6] -- [1,2,3,4,5,6]
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--
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-- 3. Records are Javascript objects, with zero or more fields, which
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-- can have different types
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let book = {title: "Foucault's pendulum", author: "Umberto Eco"}
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-- can have different types.
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-- In psci you have to write `let` in front of the function to get a
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-- top level binding.
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> let book = {title: "Foucault's pendulum", author: "Umberto Eco"}
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-- Access properties
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book.title -- "Foucault's pendulum"
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> book.title -- "Foucault's pendulum"
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getTitle b = b.title
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> let getTitle b = b.title
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-- Works on all records with a title (but doesn't require any other field)
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getTitle book -- "Foucault's pendulum"
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getTitle {title: "Weekend in Monaco", artist: "The Rippingtons"} -- "Weekend in Monaco"
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> getTitle book -- "Foucault's pendulum"
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> getTitle {title: "Weekend in Monaco", artist: "The Rippingtons"} -- "Weekend in Monaco"
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-- Can use underscores as shorthand
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> _.title book -- "Foucault's pendulum"
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-- Update a record
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changeTitle b t = b {title = t}
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changeTitle book "Ill nome della rosa" -- {title: "Ill nome della
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-- rosa", author: "Umberto Eco"}
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> let changeTitle b t = b {title = t}
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> getTitle (changeTitle book "Ill nome della rosa") -- "Ill nome della rosa"
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--
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-- 4. Functions
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sumOfSquares x y = x*x+y*y
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sumOfSquares 3 4 -- 25
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-- In psci you have to write `let` in front of the function to get a
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-- top level binding
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mod x y = x % y
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mod 3 2 -- 1
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-- In psci's multiline mode
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> let sumOfSquares :: Int -> Int -> Int
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sumOfSquares x y = x*x + y*y
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> sumOfSquares 3 4 -- 25
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> let myMod x y = x % y
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> myMod 3.0 2.0 -- 1.0
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-- Infix application of function
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3 `mod` 2 -- 1
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> 3 `mod` 2 -- 1
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-- function application have higher precedence than all other
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-- function application has higher precedence than all other
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-- operators
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sumOfSquares 3 4 * sumOfSquares 4 5 -- 1025
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> sumOfSquares 3 4 * sumOfSquares 4 5 -- 1025
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-- Conditional
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abs' n = if n>=0 then n else -n
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abs' (-3) -- 3
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> let abs' n = if n>=0 then n else -n
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> abs' (-3) -- 3
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-- Guarded equations
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abs n | n >= 0 = n
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| otherwise = -n
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> let abs'' n | n >= 0 = n
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| otherwise = -n
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-- Pattern matching
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-- Note the type signature, input is an array of numbers The pattern
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-- matching destructures and binds the array into parts
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first :: [Number] -> Number
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first (x:_) = x
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first [3,4,5] -- 3
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second :: [Number] -> Number
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second (_:y:_) = y
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second [3,4,5] -- 4
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sumTwo :: [Number] -> [Number]
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sumTwo (x:y:rest) = (x+y) : rest
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sumTwo [2,3,4,5,6] -- [5,4,5,6]
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-- Note the type signature, input is a list of numbers. The pattern matching
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-- destructures and binds the list into parts.
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-- Requires purescript-lists (Data.List)
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> let first :: forall a. List a -> a
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first (Cons x _) = x
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> first (toList [3,4,5]) -- 3
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> let second :: forall a. List a -> a
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second (Cons _ (Cons y _)) = y
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> second (toList [3,4,5]) -- 4
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> let sumTwo :: List Int -> List Int
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sumTwo (Cons x (Cons y rest)) = x + y : rest
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> fromList (sumTwo (toList [2,3,4,5,6])) :: Array Int -- [5,4,5,6]
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-- sumTwo doesn't handle when the array is empty or just have one
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-- element in which case you get an error
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-- sumTwo doesn't handle when the list is empty or there's only one element in
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-- which case you get an error.
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sumTwo [1] -- Failed pattern match
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-- Complementing patterns to match
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-- Good ol' Fibonacci
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fib 1 = 1
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fib 2 = 2
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fib x = fib (x-1) + fib (x-2)
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fib 10 -- 89
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> let fib 1 = 1
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fib 2 = 2
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fib x = fib (x-1) + fib (x-2)
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> fib 10 -- 89
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-- Use underscore to match any, where you don't care about the binding name
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isZero 0 = true
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isZero _ = false
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> let isZero 0 = true
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isZero _ = false
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-- Pattern matching on records
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ecoTitle {author = "Umberto Eco", title = t} = Just t
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ecoTitle _ = Nothing
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> let ecoTitle {author = "Umberto Eco", title = t} = Just t
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ecoTitle _ = Nothing
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ecoTitle book -- Just ("Foucault's pendulum")
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ecoTitle {title: "The Quantum Thief", author: "Hannu Rajaniemi"} -- Nothing
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> ecoTitle book -- Just ("Foucault's pendulum")
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> ecoTitle {title: "The Quantum Thief", author: "Hannu Rajaniemi"} -- Nothing
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-- ecoTitle requires both field to type check:
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ecoTitle {title: "The Quantum Thief"} -- Object does not have property author
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> ecoTitle {title: "The Quantum Thief"} -- Object lacks required property "author"
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-- Lambda expressions
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(\x -> x*x) 3 -- 9
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(\x y -> x*x + y*y) 4 5 -- 41
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sqr = \x -> x*x
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> (\x -> x*x) 3 -- 9
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> (\x y -> x*x + y*y) 4 5 -- 41
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> let sqr = \x -> x*x
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-- Currying
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add x y = x + y -- is equivalent with
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add = \x -> (\y -> x+y)
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add3 = add 3
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:t add3 -- Prim.Number -> Prim.Number
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> let myAdd x y = x + y -- is equivalent with
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> let myAdd' = \x -> \y -> x + y
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> let add3 = myAdd 3
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> :t add3 -- Prim.Int -> Prim.Int
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-- Forward and backward function composition
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-- drop 3 followed by taking 5
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(drop 3 >>> take 5) (1..20) -- [4,5,6,7,8]
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> (drop 3 >>> take 5) (1..20) -- [4,5,6,7,8]
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-- take 5 followed by dropping 3
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(drop 3 <<< take 5) (1..20) -- [4,5]
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> (drop 3 <<< take 5) (1..20) -- [4,5]
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-- Operations using higher order functions
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even x = x % 2 == 0
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filter even (1..10) -- [2,4,6,8,10]
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map (\x -> x+11) (1..5) -- [12,13,14,15,16]
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> let even x = x `mod` 2 == 0
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> filter even (1..10) -- [2,4,6,8,10]
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> map (\x -> x + 11) (1..5) -- [12,13,14,15,16]
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-- Requires purescript-foldable-traversabe (Data.Foldable)
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foldr (+) 0 (1..10) -- 55
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sum (1..10) -- 55
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product (1..10) -- 3628800
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> foldr (+) 0 (1..10) -- 55
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> sum (1..10) -- 55
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> product (1..10) -- 3628800
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-- Testing with predicate
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any even [1,2,3] -- true
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all even [1,2,3] -- false
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> any even [1,2,3] -- true
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> all even [1,2,3] -- false
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```
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