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| -rw-r--r-- | purescript.html.markdown | 117 |
1 files changed, 58 insertions, 59 deletions
diff --git a/purescript.html.markdown b/purescript.html.markdown index 6b74ac64..c848c2a4 100644 --- a/purescript.html.markdown +++ b/purescript.html.markdown @@ -6,19 +6,20 @@ contributors: - ["Thimoteus", "https://github.com/Thimoteus"] --- -PureScript is a small strongly, statically typed language compiling to Javascript. +PureScript is a small strongly, statically typed language compiling to JavaScript. -* Learn more at [http://www.purescript.org/](http://www.purescript.org/) -* Documentation: [http://pursuit.purescript.org/](http://pursuit.purescript.org/) -* Book: Purescript by Example, [https://leanpub.com/purescript/](https://leanpub.com/purescript/) +* Learn more at [https://www.purescript.org/](https://www.purescript.org/) +* Documentation: [https://pursuit.purescript.org/](https://pursuit.purescript.org/) +* Book: Purescript by Example, [https://book.purescript.org/](https://book.purescript.org/) -All the noncommented lines of code can be run in the PSCI REPL, though some will -require the `--multi-line-mode` flag. +All the noncommented lines of code can be run in the PSCi REPL, though some +will require "paste" mode (`:paste` followed by multiple lines, terminated by +^D). ```haskell -- --- 1. Primitive datatypes that corresponds to their Javascript +-- 1. Primitive datatypes that corresponds to their JavaScript -- equivalents at runtime. import Prelude @@ -39,7 +40,7 @@ import Prelude 3.0 % 2.0 -- 1.0 4.0 % 2.0 -- 0.0 -- Inspect the type of an expression in psci -:t 9.5/2.5 + 4.4 -- Prim.Number +:t 9.5/2.5 + 4.4 -- Number -- Booleans true :: Boolean -- true @@ -59,7 +60,7 @@ true && (9 >= 19 || 1 < 2) -- true -- Strings "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 "paste" mode. "Hellow\ \orld" -- "Helloworld" -- Multiline string with newlines @@ -69,26 +70,26 @@ world""" -- "Hello\nworld" "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 Int -- [1,1,2,3,5,8] [1.2,2.0,3.14] :: Array Number -- [1.2,2.0,3.14] [true, true, false] :: Array Boolean -- [true,true,false] -- [1,2, true, "false"] won't work --- `Cannot unify Prim.Int with Prim.Boolean` +-- `Cannot unify Int with Boolean` + +-- Requires purescript-arrays (Data.Array) -- Cons (prepend) 1 : [2,4,3] -- [1,2,4,3] --- Requires purescript-arrays (Data.Array) -- and purescript-maybe (Data.Maybe) - -- Safe access return Maybe a -head [1,2,3] -- Just (1) -tail [3,2,1] -- Just ([2,1]) -init [1,2,3] -- Just ([1,2]) -last [3,2,1] -- Just (1) +head [1,2,3] -- (Just 1) +tail [3,2,1] -- (Just [2,1]) +init [1,2,3] -- (Just [1,2]) +last [3,2,1] -- (Just 1) -- Array access - indexing -[3,4,5,6,7] !! 2 -- Just (5) +[3,4,5,6,7] !! 2 -- (Just 5) -- Range 1..5 -- [1,2,3,4,5] length [2,2,2] -- 3 @@ -97,31 +98,30 @@ take 3 [5,4,3,2,1] -- [5,4,3] 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. --- In psci you have to write `let` in front of the function to get a --- top level binding. -let book = {title: "Foucault's pendulum", author: "Umberto Eco"} +book = {title: "Foucault's pendulum", author: "Umberto Eco"} -- Access properties book.title -- "Foucault's pendulum" -let getTitle b = b.title +getTitle b = b.title -- Works on all records with a title (but doesn't require any other field) getTitle book -- "Foucault's pendulum" getTitle {title: "Weekend in Monaco", artist: "The Rippingtons"} -- "Weekend in Monaco" -- Can use underscores as shorthand _.title book -- "Foucault's pendulum" -- Update a record -let changeTitle b t = b {title = t} +changeTitle b t = b {title = t} getTitle (changeTitle book "Ill nome della rosa") -- "Ill nome della rosa" -- -- 4. Functions --- In psci's multiline mode -let sumOfSquares :: Int -> Int -> Int - sumOfSquares x y = x*x + y*y +-- In PSCi's paste mode +sumOfSquares :: Int -> Int -> Int +sumOfSquares x y = x*x + y*y sumOfSquares 3 4 -- 25 -let myMod x y = x % y + +myMod x y = x % y myMod 3.0 2.0 -- 1.0 -- Infix application of function 3 `mod` 2 -- 1 @@ -131,48 +131,47 @@ myMod 3.0 2.0 -- 1.0 sumOfSquares 3 4 * sumOfSquares 4 5 -- 1025 -- Conditional -let abs' n = if n>=0 then n else -n +abs' n = if n>=0 then n else -n abs' (-3) -- 3 -- Guarded equations -let abs'' n | n >= 0 = n - | otherwise = -n +-- In PSCi's paste mode +abs'' n | n >= 0 = n + | otherwise = -n -- Pattern matching -- Note the type signature, input is a list of numbers. The pattern matching -- destructures and binds the list into parts. --- Requires purescript-lists (Data.List) -let first :: forall a. List a -> a - first (Cons x _) = x -first (toList [3,4,5]) -- 3 -let second :: forall a. List a -> a - second (Cons _ (Cons y _)) = y -second (toList [3,4,5]) -- 4 -let sumTwo :: List Int -> List Int - sumTwo (Cons x (Cons y rest)) = x + y : rest -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 --- which case you get an error. -sumTwo [1] -- Failed pattern match +-- Requires purescript-lists (Data.List) and purescript-maybe (Data.Maybe) +first :: forall a. List a -> Maybe a +first (x : _) = Just x +first Nil = Nothing +first (fromFoldable [3,4,5]) -- (Just 3) + +second :: forall a. List a -> Maybe a +second Nil = Nothing +second (_ : Nil) = Nothing +second (_ : (y : _)) = Just y +second (fromFoldable [3,4,5]) -- (Just 4) -- Complementing patterns to match -- Good ol' Fibonacci -let fib 1 = 1 - fib 2 = 2 - fib x = fib (x-1) + fib (x-2) +fib 1 = 1 +fib 2 = 2 +fib x = fib (x-1) + fib (x-2) fib 10 -- 89 -- Use underscore to match any, where you don't care about the binding name -let isZero 0 = true - isZero _ = false +isZero 0 = true +isZero _ = false +isZero 9 -- false -- Pattern matching on records -let ecoTitle {author = "Umberto Eco", title = t} = Just t - ecoTitle _ = Nothing +ecoTitle {author: "Umberto Eco", title: t} = Just t +ecoTitle _ = Nothing -ecoTitle book -- Just ("Foucault's pendulum") +ecoTitle {title: "Foucault's pendulum", author: "Umberto Eco"} -- (Just "Foucault's pendulum") ecoTitle {title: "The Quantum Thief", author: "Hannu Rajaniemi"} -- Nothing -- ecoTitle requires both field to type check: ecoTitle {title: "The Quantum Thief"} -- Object lacks required property "author" @@ -180,13 +179,13 @@ ecoTitle {title: "The Quantum Thief"} -- Object lacks required property "author" -- Lambda expressions (\x -> x*x) 3 -- 9 (\x y -> x*x + y*y) 4 5 -- 41 -let sqr = \x -> x*x +sqr = \x -> x*x -- Currying -let myAdd x y = x + y -- is equivalent with -let myAdd' = \x -> \y -> x + y -let add3 = myAdd 3 -:t add3 -- Prim.Int -> Prim.Int +myAdd x y = x + y -- is equivalent with +myAdd' = \x -> \y -> x + y +add3 = myAdd 3 +:t add3 -- Int -> Int -- Forward and backward function composition -- drop 3 followed by taking 5 @@ -195,7 +194,7 @@ let add3 = myAdd 3 (drop 3 <<< take 5) (1..20) -- [4,5] -- Operations using higher order functions -let even x = x `mod` 2 == 0 +even x = x `mod` 2 == 0 filter even (1..10) -- [2,4,6,8,10] map (\x -> x + 11) (1..5) -- [12,13,14,15,16] |