Merge remote-tracking branch 'refs/remotes/adambard/master'

1 files changed, 29 insertions, 14 deletions

diff --git a/haskell.html.markdown b/haskell.html.markdown
index 08611e63..4ce1a839 100644
--- a/haskell.html.markdown
+++ b/haskell.html.markdown
@@ -81,7 +81,7 @@ not False -- True
 [5,4..1] -- [5, 4, 3, 2, 1]
 
 -- indexing into a list
-[0..] !! 5 -- 5
+[1..10] !! 3 -- 4
 
 -- You can also have infinite lists in Haskell!
 [1..] -- a list of all the natural numbers
@@ -189,16 +189,16 @@ foo = add 10 -- foo is now a function that takes a number and adds 10 to it
 foo 5 -- 15
 
 -- Another way to write the same thing
-foo = (+10)
+foo = (10+)
 foo 5 -- 15
 
 -- function composition
--- the (.) function chains functions together.
+-- the operator `.` chains functions together.
 -- For example, here foo is a function that takes a value. It adds 10 to it,
 -- multiplies the result of that by 4, and then returns the final value.
-foo = (*4) . (+10)
+foo = (4*) . (10+)
 
--- (5 + 10) * 4 = 60
+-- 4*(10 + 5) = 60
 foo 5 -- 60
 
 -- fixing precedence
@@ -222,7 +222,7 @@ even . fib $ 7 -- false
 -- 5. Type signatures
 ----------------------------------------------------
 
--- Haskell has a very strong type system, and everything has a type signature.
+-- Haskell has a very strong type system, and every valid expression has a type. 
 
 -- Some basic types:
 5 :: Integer
@@ -259,7 +259,7 @@ case args of
   _ -> putStrLn "bad args"
 
 -- Haskell doesn't have loops; it uses recursion instead.
--- map applies a function over every element in an array
+-- map applies a function over every element in a list
 
 map (*2) [1..5] -- [2, 4, 6, 8, 10]
 
@@ -279,7 +279,7 @@ foldl (\x y -> 2*x + y) 4 [1,2,3] -- 43
 -- This is the same as
 (2 * (2 * (2 * 4 + 1) + 2) + 3)
 
--- foldl is left-handed, foldr is right-
+-- foldl is left-handed, foldr is right-handed
 foldr (\x y -> 2*x + y) 4 [1,2,3] -- 16
 
 -- This is now the same as
@@ -318,7 +318,7 @@ Nothing         -- of type `Maybe a` for any `a`
 -- it is not hard to explain enough to get going.
 
 -- When a Haskell program is executed, `main` is
--- called. It must return a value of type `IO ()`. For example:
+-- called. It must return a value of type `IO a` for some type `a`. For example:
 
 main :: IO ()
 main = putStrLn $ "Hello, sky! " ++ (say Blue)
@@ -361,7 +361,7 @@ sayHello = do
 -- You can think of a value of type `IO a` as representing 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
+-- name and reuse this value using `<-`. We can also
 -- make our own action of type `IO String`:
 
 action :: IO String
@@ -401,11 +401,26 @@ main'' = do
 
 let foo = 5
 
--- You can see the type of any value with `:t`:
+-- You can see the type of any value or expression with `:t`:
 
->:t foo
+> :t foo
 foo :: Integer
 
+-- Operators, such as `+`, `:` and `$`, are functions.
+-- Their type can be inspected by putting the operator in parentheses:
+
+> :t (:)
+(:) :: a -> [a] -> [a]
+
+-- You can get additional information on any `name` using `:i`:
+
+> :i (+)
+class Num a where
+  (+) :: a -> a -> a
+  ...
+    -- Defined in ‘GHC.Num’
+infixl 6 +
+
 -- You can also run any action of type `IO ()`
 
 > sayHello
@@ -417,7 +432,7 @@ 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:
+Haskell example: an implementation of a quicksort variant in Haskell:
 
 ```haskell
 qsort [] = []
@@ -426,7 +441,7 @@ qsort (p:xs) = qsort lesser ++ [p] ++ qsort greater
           greater = filter (>= p) xs
 ```
 
-Haskell is easy to install. Get it [here](http://www.haskell.org/platform/).
+There are two popular ways to install Haskell: The traditional [Cabal-based installation](http://www.haskell.org/platform/), and the newer [Stack-based process](https://www.stackage.org/install).
 
 You can find a much gentler introduction from the excellent
 [Learn you a Haskell](http://learnyouahaskell.com/) or