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Merge pull request #4145 from emiel/emiel-fixup
[purescript/en] Updates for latest PureScript
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Adam Bard
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@ -6,19 +6,20 @@ contributors:
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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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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://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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* Learn more at [https://www.purescript.org/](https://www.purescript.org/)
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* Documentation: [https://pursuit.purescript.org/](https://pursuit.purescript.org/)
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* Book: Purescript by Example, [https://book.purescript.org/](https://book.purescript.org/)
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All the noncommented lines of code can be run in the PSCI REPL, though some will
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require the `--multi-line-mode` flag.
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All the noncommented lines of code can be run in the PSCi REPL, though some
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will require "paste" mode (`:paste` followed by multiple lines, terminated by
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^D).
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```haskell
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--
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-- 1. Primitive datatypes that corresponds to their Javascript
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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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@ -39,7 +40,7 @@ import Prelude
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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 9.5/2.5 + 4.4 -- Prim.Number
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:t 9.5/2.5 + 4.4 -- Number
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-- Booleans
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true :: Boolean -- true
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@ -59,7 +60,7 @@ true && (9 >= 19 || 1 < 2) -- true
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-- Strings
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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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-- Multiline string without newlines, to run in PSCi use "paste" mode.
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"Hellow\
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\orld" -- "Helloworld"
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-- Multiline string with newlines
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@ -69,26 +70,26 @@ world""" -- "Hello\nworld"
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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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-- 2. Arrays are JavaScript arrays, but must be homogeneous
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[1,1,2,3,5,8] :: Array Int -- [1,1,2,3,5,8]
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[1.2,2.0,3.14] :: Array Number -- [1.2,2.0,3.14]
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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.Int with Prim.Boolean`
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-- `Cannot unify Int with Boolean`
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-- Requires purescript-arrays (Data.Array)
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-- Cons (prepend)
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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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-- Array 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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@ -97,31 +98,30 @@ 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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-- 3. Records are JavaScript objects, with zero or more fields, which
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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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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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let getTitle b = b.title
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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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-- 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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let changeTitle b t = b {title = t}
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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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-- 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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-- In PSCi's paste mode
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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 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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@ -131,48 +131,47 @@ myMod 3.0 2.0 -- 1.0
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sumOfSquares 3 4 * sumOfSquares 4 5 -- 1025
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-- Conditional
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let abs' n = if n>=0 then n else -n
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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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let abs'' n | n >= 0 = n
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| otherwise = -n
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-- In PSCi's paste mode
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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 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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-- Requires purescript-lists (Data.List) and purescript-maybe (Data.Maybe)
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first :: forall a. List a -> Maybe a
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first (x : _) = Just x
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first Nil = Nothing
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first (fromFoldable [3,4,5]) -- (Just 3)
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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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second :: forall a. List a -> Maybe a
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second Nil = Nothing
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second (_ : Nil) = Nothing
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second (_ : (y : _)) = Just y
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second (fromFoldable [3,4,5]) -- (Just 4)
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-- Complementing patterns to match
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-- Good ol' Fibonacci
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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 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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let isZero 0 = true
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isZero _ = false
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isZero 0 = true
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isZero _ = false
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isZero 9 -- false
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-- Pattern matching on records
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let ecoTitle {author = "Umberto Eco", title = t} = Just t
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ecoTitle _ = Nothing
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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: "Foucault's pendulum", author: "Umberto Eco"} -- (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 lacks required property "author"
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@ -180,13 +179,13 @@ 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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let sqr = \x -> x*x
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sqr = \x -> x*x
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-- Currying
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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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myAdd x y = x + y -- is equivalent with
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myAdd' = \x -> \y -> x + y
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add3 = myAdd 3
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:t add3 -- Int -> Int
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-- Forward and backward function composition
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-- drop 3 followed by taking 5
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@ -195,7 +194,7 @@ let add3 = myAdd 3
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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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let even x = x `mod` 2 == 0
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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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