Merge remote-tracking branch 'adambard/master' into adambard/master-cn

1 files changed, 63 insertions, 47 deletions

diff --git a/haskell.html.markdown b/haskell.html.markdown
index be7d8669..369b1b20 100644
--- a/haskell.html.markdown
+++ b/haskell.html.markdown
@@ -1,17 +1,17 @@
 ---
-language: haskell
+language: Haskell
 contributors:
     - ["Adit Bhargava", "http://adit.io"]
 ---
 
-Haskell was designed as a practical, purely functional programming language. It's famous for
-its monads and its type system, but I keep coming back to it because of its elegance. Haskell
-makes coding a real joy for me.
+Haskell was designed as a practical, purely functional programming
+language. It's famous for its monads and its type system, but I keep coming back
+to it because of its elegance. Haskell makes coding a real joy for me.
 
 ```haskell
 -- Single line comments start with two dashes.
 {- Multiline comments can be enclosed
-en a block like this.
+in a block like this.
 -}
 
 ----------------------------------------------------
@@ -59,6 +59,7 @@ not False -- True
 "Hello " ++ "world!" -- "Hello world!"
 
 -- A string is a list of characters
+['H', 'e', 'l', 'l', 'o'] -- "Hello"
 "This is a string" !! 0 -- 'T'
 
 
@@ -67,10 +68,21 @@ not False -- True
 ----------------------------------------------------
 
 -- Every element in a list must have the same type.
--- Two lists that are the same
+-- These two lists are the same:
 [1, 2, 3, 4, 5]
 [1..5]
 
+-- Ranges are versatile.
+['A'..'F'] -- "ABCDEF"
+
+-- You can create a step in a range.
+[0,2..10] -- [0, 2, 4, 6, 8, 10]
+[5..1] -- This doesn't work because Haskell defaults to incrementing.
+[5,4..1] -- [5, 4, 3, 2, 1]
+
+-- indexing into a list
+[0..] !! 5 -- 5
+
 -- You can also have infinite lists in Haskell!
 [1..] -- a list of all the natural numbers
 
@@ -84,15 +96,12 @@ not False -- True
 -- rest of the elements of this "infinite" list don't exist yet! Haskell won't
 -- actually evaluate them until it needs to.
 
-- joining two lists
+-- joining two lists
 [1..5] ++ [6..10]
 
 -- adding to the head of a list
 0:[1..5] -- [0, 1, 2, 3, 4, 5]
 
--- indexing into a list
-[0..] !! 5 -- 5
-
 -- more list operations
 head [1..5] -- 1
 tail [1..5] -- [2, 3, 4, 5]
@@ -110,7 +119,7 @@ last [1..5] -- 5
 -- A tuple:
 ("haskell", 1)
 
--- accessing elements of a tuple
+-- accessing elements of a pair (i.e. a tuple of length 2)
 fst ("haskell", 1) -- "haskell"
 snd ("haskell", 1) -- 1
 
@@ -131,7 +140,7 @@ add 1 2 -- 3
 -- with backticks:
 1 `add` 2 -- 3
 
--- You can also define functions that have no characters! This lets
+-- You can also define functions that have no letters! This lets
 -- you define your own operators! Here's an operator that does
 -- integer division
 (//) a b = a `div` b
@@ -139,12 +148,12 @@ add 1 2 -- 3
 
 -- Guards: an easy way to do branching in functions
 fib x
-  | x < 2 = x
+  | x < 2 = 1
   | otherwise = fib (x - 1) + fib (x - 2)
 
 -- Pattern matching is similar. Here we have given three different
 -- definitions for fib. Haskell will automatically call the first
--- function that matches the pattern of the value. 
+-- function that matches the pattern of the value.
 fib 1 = 1
 fib 2 = 2
 fib x = fib (x - 1) + fib (x - 2)
@@ -171,8 +180,8 @@ foldl1 (\acc x -> acc + x) [1..5] -- 15
 -- 4. More functions
 ----------------------------------------------------
 
--- currying: if you don't pass in all the arguments to a function,
--- it gets "curried". That means it returns a function that takes the 
+-- partial application: if you don't pass in all the arguments to a function,
+-- it gets "partially applied". That means it returns a function that takes the
 -- rest of the arguments.
 
 add a b = a + b
@@ -193,16 +202,21 @@ foo = (*5) . (+10)
 foo 5 -- 75
 
 -- fixing precedence
--- Haskell has another function called `$`. This changes the precedence
--- so that everything to the left of it gets computed first and then applied
--- to everything on the right. You can use `.` and `$` to get rid of a lot
--- of parentheses:
+-- Haskell has another operator called `$`. This operator applies a function 
+-- to a given parameter. In contrast to standard function application, which 
+-- has highest possible priority of 10 and is left-associative, the `$` operator 
+-- has priority of 0 and is right-associative. Such a low priority means that
+-- the expression on its right is applied as the parameter to the function on its left.
 
 -- before
-(even (fib 7)) -- true
+even (fib 7) -- false
+
+-- equivalently
+even $ fib 7 -- false
+
+-- composing functions
+even . fib $ 7 -- false
 
--- after
-even . fib $ 7 -- true
 
 ----------------------------------------------------
 -- 5. Type signatures
@@ -227,24 +241,24 @@ double :: Integer -> Integer
 double x = x * 2
 
 ----------------------------------------------------
--- 6. Control Flow and If Statements
+-- 6. Control Flow and If Expressions
 ----------------------------------------------------
 
--- if statements
+-- if expressions
 haskell = if 1 == 1 then "awesome" else "awful" -- haskell = "awesome"
 
--- if statements can be on multiple lines too, indentation is important
+-- if expressions can be on multiple lines too, indentation is important
 haskell = if 1 == 1
             then "awesome"
             else "awful"
 
--- case statements: Here's how you could parse command line arguments
+-- case expressions: Here's how you could parse command line arguments
 case args of
   "help" -> printHelp
   "start" -> startProgram
   _ -> putStrLn "bad args"
 
--- Haskell doesn't have loops because it uses recursion instead.
+-- Haskell doesn't have loops; it uses recursion instead.
 -- map applies a function over every element in an array
 
 map (*2) [1..5] -- [2, 4, 6, 8, 10]
@@ -269,7 +283,7 @@ foldl (\x y -> 2*x + y) 4 [1,2,3] -- 43
 foldr (\x y -> 2*x + y) 4 [1,2,3] -- 16
 
 -- This is now the same as
-(2 * 3 + (2 * 2 + (2 * 1 + 4)))
+(2 * 1 + (2 * 2 + (2 * 3 + 4)))
 
 ----------------------------------------------------
 -- 7. Data Types
@@ -303,17 +317,17 @@ Nothing         -- of type `Maybe a` for any `a`
 -- While IO can't be explained fully without explaining monads,
 -- it is not hard to explain enough to get going.
 
--- When a Haskell program is executed, the function `main` is
+-- When a Haskell program is executed, `main` is
 -- called. It must return a value of type `IO ()`. For example:
 
 main :: IO ()
-main = putStrLn $ "Hello, sky! " ++ (say Blue) 
+main = putStrLn $ "Hello, sky! " ++ (say Blue)
 -- putStrLn has type String -> IO ()
 
--- It is easiest to do IO if you can implement your program as 
--- a function from String to String. The function 
+-- It is easiest to do IO if you can implement your program as
+-- a function from String to String. The function
 --    interact :: (String -> String) -> IO ()
--- inputs some text, runs a function on it, and prints out the 
+-- inputs some text, runs a function on it, and prints out the
 -- output.
 
 countLines :: String -> String
@@ -327,43 +341,43 @@ main' = interact countLines
 -- the `do` notation to chain actions together. For example:
 
 sayHello :: IO ()
-sayHello = do 
+sayHello = do
    putStrLn "What is your name?"
-   name <- getLine -- this gets a line and gives it the name "input"
+   name <- getLine -- this gets a line and gives it the name "name"
    putStrLn $ "Hello, " ++ name
-   
+
 -- Exercise: write your own version of `interact` that only reads
 --           one line of input.
-   
+
 -- The code in `sayHello` will never be executed, however. The only
--- action that ever gets executed is the value of `main`. 
--- To run `sayHello` comment out the above definition of `main` 
+-- action that ever gets executed is the value of `main`.
+-- To run `sayHello` comment out the above definition of `main`
 -- and replace it with:
 --   main = sayHello
 
--- Let's understand better how the function `getLine` we just 
+-- Let's understand better how the function `getLine` we just
 -- used works. Its type is:
 --    getLine :: IO String
 -- You can think of a value of type `IO a` as representing a
--- computer program that will generate a value of type `a` 
+-- computer program that will generate a value of type `a`
 -- when executed (in addition to anything else it does). We can
--- store and reuse this value using `<-`. We can also 
+-- store and reuse this value using `<-`. We can also
 -- make our own action of type `IO String`:
 
 action :: IO String
 action = do
    putStrLn "This is a line. Duh"
-   input1 <- getLine 
+   input1 <- getLine
    input2 <- getLine
    -- The type of the `do` statement is that of its last line.
-   -- `return` is not a keyword, but merely a function 
+   -- `return` is not a keyword, but merely a function
    return (input1 ++ "\n" ++ input2) -- return :: String -> IO String
 
 -- We can use this just like we used `getLine`:
 
 main'' = do
     putStrLn "I will echo two lines!"
-    result <- action 
+    result <- action
     putStrLn result
     putStrLn "This was all, folks!"
 
@@ -401,7 +415,9 @@ Hello, Friend!
 
 ```
 
-There's a lot more to Haskell, including typeclasses and monads. These are the big ideas that make Haskell such fun to code in. I'll leave you with one final Haskell example: an implementation of quicksort in Haskell:
+There's a lot more to Haskell, including typeclasses and monads. These are the
+big ideas that make Haskell such fun to code in. I'll leave you with one final
+Haskell example: an implementation of quicksort in Haskell:
 
 ```haskell
 qsort [] = []