readded haskell syntax highlighting, added line about running examples in psci, removed >'s

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thimoteus 2015-10-13 01:25:56 -07:00
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@ -11,142 +11,145 @@ PureScript is a small strongly, statically typed language compiling to Javascrip
* Documentation: [http://pursuit.purescript.org/](http://pursuit.purescript.org/) * Documentation: [http://pursuit.purescript.org/](http://pursuit.purescript.org/)
* Book: Purescript by Example, [https://leanpub.com/purescript/](https://leanpub.com/purescript/) * Book: Purescript by Example, [https://leanpub.com/purescript/](https://leanpub.com/purescript/)
```purescript All the noncommented lines of code can be run in the PSCI REPL, though some will
require the `--multi-line-mode` flag.
```haskell
-- --
-- 1. Primitive datatypes that corresponds to their Javascript -- 1. Primitive datatypes that corresponds to their Javascript
-- equivalents at runtime. -- equivalents at runtime.
> import Prelude import Prelude
-- Numbers -- Numbers
> 1.0 + 7.2*5.5 :: Number -- 40.6 1.0 + 7.2*5.5 :: Number -- 40.6
-- Ints -- Ints
> 1 + 2*5 :: Int -- 11 1 + 2*5 :: Int -- 11
-- Types are inferred, so the following works fine -- Types are inferred, so the following works fine
> 9.0/2.5 + 4.4 -- 8.0 9.0/2.5 + 4.4 -- 8.0
-- But Ints and Numbers don't mix, so the following won't -- But Ints and Numbers don't mix, so the following won't
> 5/2 + 2.5 -- Expression 2.5 does not have type Int 5/2 + 2.5 -- Expression 2.5 does not have type Int
-- Hexadecimal literals -- Hexadecimal literals
> 0xff + 1 -- 256 0xff + 1 -- 256
-- Unary negation -- Unary negation
> 6 * -3 -- -18 6 * -3 -- -18
> 6 * negate 3 -- -18 6 * negate 3 -- -18
-- Modulus, from purescript-math (Math) -- Modulus, from purescript-math (Math)
> 3.0 % 2.0 -- 1.0 3.0 % 2.0 -- 1.0
> 4.0 % 2.0 -- 0.0 4.0 % 2.0 -- 0.0
-- Inspect the type of an expression in psci -- Inspect the type of an expression in psci
> :t 9.5/2.5 + 4.4 -- Prim.Number :t 9.5/2.5 + 4.4 -- Prim.Number
-- Booleans -- Booleans
> true :: Boolean -- true true :: Boolean -- true
> false :: Boolean -- false false :: Boolean -- false
-- Negation -- Negation
> not true -- false not true -- false
> 23 == 23 -- true 23 == 23 -- true
> 1 /= 4 -- true 1 /= 4 -- true
> 1 >= 4 -- false 1 >= 4 -- false
-- Comparisions < <= > >= -- Comparisions < <= > >=
-- are defined in terms of compare -- are defined in terms of compare
> compare 1 2 -- LT compare 1 2 -- LT
> compare 2 2 -- EQ compare 2 2 -- EQ
> compare 3 2 -- GT compare 3 2 -- GT
-- Conjunction and Disjunction -- Conjunction and Disjunction
> true && (9 >= 19 || 1 < 2) -- true true && (9 >= 19 || 1 < 2) -- true
-- Strings -- Strings
> "Hellow" :: String -- "Hellow" "Hellow" :: String -- "Hellow"
-- Multiline string without newlines, to run in psci use the --multi-line-mode flag -- Multiline string without newlines, to run in psci use the --multi-line-mode flag
> "Hellow\ "Hellow\
\orld" -- "Helloworld" \orld" -- "Helloworld"
-- Multiline string with newlines -- Multiline string with newlines
> """Hello """Hello
world""" -- "Hello\nworld" world""" -- "Hello\nworld"
-- Concatenate -- Concatenate
> "such " ++ "amaze" -- "such amaze" "such " ++ "amaze" -- "such amaze"
-- --
-- 2. Arrays are Javascript arrays, but must be homogeneous -- 2. Arrays are Javascript arrays, but must be homogeneous
> [1,1,2,3,5,8] :: Array Number -- [1,1,2,3,5,8] [1,1,2,3,5,8] :: Array Number -- [1,1,2,3,5,8]
> [true, true, false] :: Array Boolean -- [true,true,false] [true, true, false] :: Array Boolean -- [true,true,false]
-- [1,2, true, "false"] won't work -- [1,2, true, "false"] won't work
-- `Cannot unify Prim.Int with Prim.Boolean` -- `Cannot unify Prim.Int with Prim.Boolean`
-- Cons (prepend) -- Cons (prepend)
> 1 : [2,4,3] -- [1,2,4,3] 1 : [2,4,3] -- [1,2,4,3]
-- Requires purescript-arrays (Data.Array) -- Requires purescript-arrays (Data.Array)
-- and purescript-maybe (Data.Maybe) -- and purescript-maybe (Data.Maybe)
-- Safe access return Maybe a -- Safe access return Maybe a
> head [1,2,3] -- Just (1) head [1,2,3] -- Just (1)
> tail [3,2,1] -- Just ([2,1]) tail [3,2,1] -- Just ([2,1])
> init [1,2,3] -- Just ([1,2]) init [1,2,3] -- Just ([1,2])
> last [3,2,1] -- Just (1) last [3,2,1] -- Just (1)
-- Random access - indexing -- Random access - indexing
> [3,4,5,6,7] !! 2 -- Just (5) [3,4,5,6,7] !! 2 -- Just (5)
-- Range -- Range
> 1..5 -- [1,2,3,4,5] 1..5 -- [1,2,3,4,5]
> length [2,2,2] -- 3 length [2,2,2] -- 3
> drop 3 [5,4,3,2,1] -- [2,1] drop 3 [5,4,3,2,1] -- [2,1]
> take 3 [5,4,3,2,1] -- [5,4,3] take 3 [5,4,3,2,1] -- [5,4,3]
> append [1,2,3] [4,5,6] -- [1,2,3,4,5,6] append [1,2,3] [4,5,6] -- [1,2,3,4,5,6]
-- --
-- 3. Records are Javascript objects, with zero or more fields, which -- 3. Records are Javascript objects, with zero or more fields, which
-- can have different types. -- can have different types.
-- In psci you have to write `let` in front of the function to get a -- In psci you have to write `let` in front of the function to get a
-- top level binding. -- top level binding.
> let book = {title: "Foucault's pendulum", author: "Umberto Eco"} let book = {title: "Foucault's pendulum", author: "Umberto Eco"}
-- Access properties -- Access properties
> book.title -- "Foucault's pendulum" book.title -- "Foucault's pendulum"
> let getTitle b = b.title let getTitle b = b.title
-- Works on all records with a title (but doesn't require any other field) -- Works on all records with a title (but doesn't require any other field)
> getTitle book -- "Foucault's pendulum" getTitle book -- "Foucault's pendulum"
> getTitle {title: "Weekend in Monaco", artist: "The Rippingtons"} -- "Weekend in Monaco" getTitle {title: "Weekend in Monaco", artist: "The Rippingtons"} -- "Weekend in Monaco"
-- Can use underscores as shorthand -- Can use underscores as shorthand
> _.title book -- "Foucault's pendulum" _.title book -- "Foucault's pendulum"
-- Update a record -- Update a record
> let changeTitle b t = b {title = t} let changeTitle b t = b {title = t}
> getTitle (changeTitle book "Ill nome della rosa") -- "Ill nome della rosa" getTitle (changeTitle book "Ill nome della rosa") -- "Ill nome della rosa"
-- --
-- 4. Functions -- 4. Functions
-- In psci's multiline mode -- In psci's multiline mode
> let sumOfSquares :: Int -> Int -> Int let sumOfSquares :: Int -> Int -> Int
sumOfSquares x y = x*x + y*y sumOfSquares x y = x*x + y*y
> sumOfSquares 3 4 -- 25 sumOfSquares 3 4 -- 25
> let myMod x y = x % y let myMod x y = x % y
> myMod 3.0 2.0 -- 1.0 myMod 3.0 2.0 -- 1.0
-- Infix application of function -- Infix application of function
> 3 `mod` 2 -- 1 3 `mod` 2 -- 1
-- function application has higher precedence than all other -- function application has higher precedence than all other
-- operators -- operators
> sumOfSquares 3 4 * sumOfSquares 4 5 -- 1025 sumOfSquares 3 4 * sumOfSquares 4 5 -- 1025
-- Conditional -- Conditional
> let abs' n = if n>=0 then n else -n let abs' n = if n>=0 then n else -n
> abs' (-3) -- 3 abs' (-3) -- 3
-- Guarded equations -- Guarded equations
> let abs'' n | n >= 0 = n let abs'' n | n >= 0 = n
| otherwise = -n | otherwise = -n
-- Pattern matching -- Pattern matching
-- Note the type signature, input is a list of numbers. The pattern matching -- Note the type signature, input is a list of numbers. The pattern matching
-- destructures and binds the list into parts. -- destructures and binds the list into parts.
-- Requires purescript-lists (Data.List) -- Requires purescript-lists (Data.List)
> let first :: forall a. List a -> a let first :: forall a. List a -> a
first (Cons x _) = x first (Cons x _) = x
> first (toList [3,4,5]) -- 3 first (toList [3,4,5]) -- 3
> let second :: forall a. List a -> a let second :: forall a. List a -> a
second (Cons _ (Cons y _)) = y second (Cons _ (Cons y _)) = y
> second (toList [3,4,5]) -- 4 second (toList [3,4,5]) -- 4
> let sumTwo :: List Int -> List Int let sumTwo :: List Int -> List Int
sumTwo (Cons x (Cons y rest)) = x + y : rest sumTwo (Cons x (Cons y rest)) = x + y : rest
> fromList (sumTwo (toList [2,3,4,5,6])) :: Array Int -- [5,4,5,6] fromList (sumTwo (toList [2,3,4,5,6])) :: Array Int -- [5,4,5,6]
-- sumTwo doesn't handle when the list is empty or there's only one element in -- sumTwo doesn't handle when the list is empty or there's only one element in
-- which case you get an error. -- which case you get an error.
@ -154,55 +157,55 @@ sumTwo [1] -- Failed pattern match
-- Complementing patterns to match -- Complementing patterns to match
-- Good ol' Fibonacci -- Good ol' Fibonacci
> let fib 1 = 1 let fib 1 = 1
fib 2 = 2 fib 2 = 2
fib x = fib (x-1) + fib (x-2) fib x = fib (x-1) + fib (x-2)
> fib 10 -- 89 fib 10 -- 89
-- Use underscore to match any, where you don't care about the binding name -- Use underscore to match any, where you don't care about the binding name
> let isZero 0 = true let isZero 0 = true
isZero _ = false isZero _ = false
-- Pattern matching on records -- Pattern matching on records
> let ecoTitle {author = "Umberto Eco", title = t} = Just t let ecoTitle {author = "Umberto Eco", title = t} = Just t
ecoTitle _ = Nothing ecoTitle _ = Nothing
> ecoTitle book -- Just ("Foucault's pendulum") ecoTitle book -- Just ("Foucault's pendulum")
> ecoTitle {title: "The Quantum Thief", author: "Hannu Rajaniemi"} -- Nothing ecoTitle {title: "The Quantum Thief", author: "Hannu Rajaniemi"} -- Nothing
-- ecoTitle requires both field to type check: -- ecoTitle requires both field to type check:
> ecoTitle {title: "The Quantum Thief"} -- Object lacks required property "author" ecoTitle {title: "The Quantum Thief"} -- Object lacks required property "author"
-- Lambda expressions -- Lambda expressions
> (\x -> x*x) 3 -- 9 (\x -> x*x) 3 -- 9
> (\x y -> x*x + y*y) 4 5 -- 41 (\x y -> x*x + y*y) 4 5 -- 41
> let sqr = \x -> x*x let sqr = \x -> x*x
-- Currying -- Currying
> let myAdd x y = x + y -- is equivalent with let myAdd x y = x + y -- is equivalent with
> let myAdd' = \x -> \y -> x + y let myAdd' = \x -> \y -> x + y
> let add3 = myAdd 3 let add3 = myAdd 3
> :t add3 -- Prim.Int -> Prim.Int :t add3 -- Prim.Int -> Prim.Int
-- Forward and backward function composition -- Forward and backward function composition
-- drop 3 followed by taking 5 -- drop 3 followed by taking 5
> (drop 3 >>> take 5) (1..20) -- [4,5,6,7,8] (drop 3 >>> take 5) (1..20) -- [4,5,6,7,8]
-- take 5 followed by dropping 3 -- take 5 followed by dropping 3
> (drop 3 <<< take 5) (1..20) -- [4,5] (drop 3 <<< take 5) (1..20) -- [4,5]
-- Operations using higher order functions -- Operations using higher order functions
> let even x = x `mod` 2 == 0 let even x = x `mod` 2 == 0
> filter even (1..10) -- [2,4,6,8,10] filter even (1..10) -- [2,4,6,8,10]
> map (\x -> x + 11) (1..5) -- [12,13,14,15,16] map (\x -> x + 11) (1..5) -- [12,13,14,15,16]
-- Requires purescript-foldable-traversabe (Data.Foldable) -- Requires purescript-foldable-traversabe (Data.Foldable)
> foldr (+) 0 (1..10) -- 55 foldr (+) 0 (1..10) -- 55
> sum (1..10) -- 55 sum (1..10) -- 55
> product (1..10) -- 3628800 product (1..10) -- 3628800
-- Testing with predicate -- Testing with predicate
> any even [1,2,3] -- true any even [1,2,3] -- true
> all even [1,2,3] -- false all even [1,2,3] -- false
``` ```