Update various examples

* `let` no longer required in PSCi
* Properly emit output, `(Just 1)` vs `Just (1)`
* Remove `sumTwo` as it is too convoluted of an example

purescript.html.markdown

@@ -84,12 +84,12 @@ world""" -- "Hello\nworld"
 
 -- and purescript-maybe (Data.Maybe)
 -- 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)
 -- 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
@@ -100,29 +100,28 @@ append [1,2,3] [4,5,6] -- [1,2,3,4,5,6]
 --
 -- 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
+book = {title: "Foucault's pendulum", author: "Umberto Eco"}
--- top level binding.
-let 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
+-- In PSCi's paste mode
-let sumOfSquares :: Int -> Int -> Int
+sumOfSquares :: Int -> Int -> Int
-    sumOfSquares x y = x*x + y*y
+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
@@ -132,48 +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
+-- In PSCi's paste mode
-            | otherwise = -n
+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)
+-- Requires purescript-lists (Data.List) and purescript-maybe (Data.Maybe)
-let first :: forall a. List a -> a
+first :: forall a. List a -> Maybe a
-    first (Cons x _) = x
+first (x : _) = Just x
-first (toList [3,4,5]) -- 3
+first Nil = Nothing
-let second :: forall a. List a -> a
+first (fromFoldable [3,4,5]) -- (Just 3)
-    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
+second :: forall a. List a -> Maybe a
--- which case you get an error.
+second Nil = Nothing
-sumTwo [1] -- Failed pattern match
+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 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
 
 -- Use underscore to match any, where you don't care about the binding name
-let isZero 0 = true
+isZero 0 = true
-    isZero _ = false
+isZero _ = false
+isZero 9 -- false
 
 -- Pattern matching on records
-let ecoTitle {author = "Umberto Eco", title = t} = Just t
+ecoTitle {author: "Umberto Eco", title: t} = Just t
-    ecoTitle _ = Nothing
+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"
@@ -181,13 +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
+myAdd x y = x + y -- is equivalent with
-let myAdd' = \x -> \y -> x + y
+myAdd' = \x -> \y -> x + y
-let add3 = myAdd 3
+add3 = myAdd 3
-:t add3 -- Prim.Int -> Prim.Int
+:t add3 -- Int -> Int
 
 -- Forward and backward function composition
 -- drop 3 followed by taking 5
@@ -196,7 +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]