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authorHunter Stevens <onebree@gmail.com>2016-02-15 17:47:35 -0500
committerHunter Stevens <onebree@gmail.com>2016-02-15 17:47:35 -0500
commitd0b067b140d3d351ae9dee0b3e542935b7ca35d4 (patch)
treeb83501b5b82240663029d7382f873fb369ea81c7 /haskell.html.markdown
parentcffb7e6770b517a620115b3a9e1f82ca1dd82a98 (diff)
parentcd16626c8f64a29d8235bd0ab21c7a32e248928f (diff)
Resolve conflicts from merge
Diffstat (limited to 'haskell.html.markdown')
-rw-r--r--haskell.html.markdown43
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