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[[Category:How to]]
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== Haskell Cookbook ==
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* [[Cookbook/Compilers and interpreters|Haskell compilers and interpreters]]
* [[Cookbook/Strings|Strings]]
 
 
* [[Cookbook/Numbers|Numbers]]
 
* [[Cookbook/Numbers|Numbers]]
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* [[Cookbook/Lists and strings|Lists and strings]]
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* [[Cookbook/Other data structures|Other data structures]]
 
* [[Cookbook/Dates And Time|Dates and time]]
 
* [[Cookbook/Dates And Time|Dates and time]]
* [[Cookbook/Lists|Lists]]
 
* [[Cookbook/Other data structures|Other data structures]]
 
 
* [[Cookbook/Pattern matching|Pattern matching]]
 
* [[Cookbook/Pattern matching|Pattern matching]]
 
* [[Cookbook/Interactivity|Interactivity]]
 
* [[Cookbook/Interactivity|Interactivity]]
 
* [[Cookbook/Files|Files]]
 
* [[Cookbook/Files|Files]]
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* [[Cookbook/Network programming|Network programming]]
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* [[Cookbook/XML|XML]]
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* [[Cookbook/Databases access|Databases access]]
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* [[Cookbook/Graphical user interfaces|Graphical user interfaces]]
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* [[Cookbook/PDF files|PDF files]]
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* [[Cookbook/FFI|FFI]]
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* [[Cookbook/Testing|Testing]]
   
{{Template:Anonymousdraft}}
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== Similar projects for other programming languages ==
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* [http://cl-cookbook.sourceforge.net/ Common Lisp Cookbook]
'''We need to start a Haskell centered cookbook (aka, not a [http://pleac.sourceforge.net/ PLEAC] clone)
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* [http://pleac.sourceforge.net/ PLEAC]
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* [http://www.zenspider.com/Languages/Ruby/Cookbook/index.html Ruby Cookbook]
This page is based on the Scheme Cookbook at
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* [http://schemecookbook.org/Cookbook/WebHome Scheme Cookbook]
http://schemecookbook.org/Cookbook/WebHome'''
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* [http://fssnip.net/ F# Snippets]
== Prelude ==
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[[Category:FAQ]]
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[[Category:How to]]
A lot of functions are defined in the "[http://www.haskell.org/hoogle/?q=Prelude Prelude]". Also, if you ever want to search for a function, based on the name, type or module, take a look at the excellent [http://www.haskell.org/hoogle/ Hoogle]. This is for a lot of people a must-have while debugging and writing Haskell programs.
 
 
== GHCi/Hugs ==
 
=== GHCi interaction ===
 
To start GHCi from a command prompt, simply type `ghci'
 
 
$ ghci
 
___ ___ _
 
/ _ \ /\ /\/ __(_)
 
/ /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98.
 
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
 
\____/\/ /_/\____/|_| Type :? for help.
 
 
Loading package base ... linking ... done.
 
Prelude>
 
 
[http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html Prelude] is the "base" library of Haskell.
 
 
To create variables at the GHCi prompt, use `let'
 
<haskell>
 
Prelude> let x = 5
 
Prelude> x
 
5
 
Prelude> let y = 3
 
Prelude> y
 
3
 
Prelude> x + y
 
8
 
</haskell>
 
 
`let' is also the way to create simple functions at the GHCi prompt
 
<haskell>
 
Prelude> let fact n = product [1..n]
 
Prelude> fact 5
 
120
 
</haskell>
 
 
 
=== Checking Types ===
 
To check the type of an expression or function, use the command `:t'
 
<haskell>
 
Prelude> :t x
 
x :: Integer
 
Prelude> :t "Hello"
 
"Hello" :: [Char]
 
</haskell>
 
Haskell has the following types defined in the [http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html Standard Prelude].
 
<haskell>
 
Int -- bounded, word-sized integers
 
Integer -- unbounded integers
 
Double -- floating point values
 
Char -- characters
 
String -- equivalent to [Char], strings are lists of characters
 
() -- the unit type
 
Bool -- booleans
 
[a] -- lists
 
(a,b) -- tuples / product types
 
Either a b -- sum types
 
Maybe a -- optional values
 
</haskell>
 
 
 
 
 
 
 
 
 
 
 
 
== Network programming ==
 
The following example makes use of the Network and System.IO libraries to open
 
a socket connection to Google and retrieve the Google home page.
 
 
<haskell>
 
import Network;
 
import System.IO;
 
 
main = withSocketsDo $ do
 
h <- connectTo "www.google.com" (PortNumber 80)
 
hSetBuffering h LineBuffering
 
hPutStr h "GET / HTTP/1.1\nhost: www.google.com\n\n"
 
contents <- hGetContents h
 
putStrLn contents
 
hClose h
 
</haskell>
 
== XML ==
 
=== Libraries ===
 
There are multiple libraries available. In my own (limited) experience, I could only get [[HXT]] to do everything I wanted. It does make heavy use of [[http://haskell.org/arrows/ Arrows]].
 
 
=== Parsing XML ===
 
 
TODO
 
 
== Databases access ==
 
There are two packages you can use to connect to MySQL, PostgreSQL, Sqlite3 and ODBC databases: [http://software.complete.org/software/projects/show/hdbc HDBC] and Hsql
 
 
=== MySQL ===
 
 
TODO
 
 
=== PostgreSQL ===
 
 
TODO
 
 
=== SQLite ===
 
Suppose you have created a 'test.db' database like this,
 
 
$ sqlite3 test.db "create table t1 (t1key INTEGER PRIMARY KEY,data TEXT,num double,timeEnter DATE);"
 
 
$ sqlite3 test.db "insert into t1 (data,num) values ('This is sample data',3);"
 
 
$ sqlite3 test.db "insert into t1 (data,num) values ('More sample data',6);"
 
 
$ sqlite3 test.db "insert into t1 (data,num) values ('And a little more',9);"
 
 
Using HDBC and HDBC-sqlite3 packages, you can connect and query it like this:
 
<haskell>
 
import Control.Monad
 
import Database.HDBC
 
import Database.HDBC.Sqlite3
 
 
main = do conn <- connectSqlite3 "test.db"
 
rows <- quickQuery' conn "SELECT * from t1" []
 
forM_ rows $ \row -> putStrLn $ show row
 
</haskell>
 
 
 
$ ghc --make sqlite.hs
 
 
$ ./sqlite
 
 
output:
 
 
[SqlString "1",SqlString "This is sample data",SqlString "3.0",SqlNull]
 
 
[SqlString "2",SqlString "More sample data",SqlString "6.0",SqlNull]
 
 
[SqlString "3",SqlString "And a little more",SqlString "9.0",SqlNull]
 
 
== Graphical user interfaces ==
 
 
=== wxHaskell ===
 
[[WxHaskell|wxHaskell]] is a portable and native GUI library for Haskell based on the wxWidgets Library.
 
 
Hello World example:
 
 
<haskell>
 
module Main where
 
import Graphics.UI.WX
 
 
main :: IO ()
 
main
 
= start hello
 
 
hello :: IO ()
 
hello
 
= do f <- frame [text := "Hello!"]
 
quit <- button f [text := "Quit", on command := close f]
 
set f [layout := widget quit]
 
</haskell>
 
 
This code was taken from [[WxHaskell/Quick_start | "a quick start with wxHaskell"]].
 
 
=== Gtk2Hs ===
 
[http://haskell.org/gtk2hs/screenshots/ Gtk2Hs] is a GUI Library for
 
Haskell based on GTK. [http://home.telfort.nl/sp969709/gtk2hs/ Gtk2Hs Tutorial].
 
 
Hello world example:
 
 
<haskell>
 
import Graphics.UI.Gtk
 
 
main :: IO ()
 
main = do
 
initGUI
 
w <- windowNew
 
b <- buttonNew
 
set b [buttonLabel := "Quit"]
 
onClicked b $ widgetDestroy w
 
set w [windowTitle := "Hello", containerBorderWidth := 10]
 
containerAdd w b
 
onDestroy w mainQuit
 
widgetShowAll w
 
mainGUI
 
</haskell>
 
 
For more examples, see: [[Applications and libraries/Games]]
 
 
=== HOpenGL ===
 
[http://www.haskell.org/HOpenGL/ HOpenGL] is a Haskell binding for the OpenGL graphics API (GL 1.2.1 / GLU 1.3) and the portable OpenGL utility toolkit GLUT.
 
There is a Haskell OpenGL Tetris program at
 
[[http://haskell-tetris.pbwiki.com/Main]] by Jim.
 
 
See also: [[Applications and libraries/Games]]
 
 
=== SDL ===
 
There are some Haskell bindings to [http://libsdl.org/ SDL] at [http://hackage.haskell.org/packages/archive/pkg-list.html Hackage].
 
 
== PDF files ==
 
 
For the following recipes you need to install [http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HPDF HPDF].
 
 
=== Creating an empty PDF file ===
 
 
The following code creates an empty PDF file with the name "test1.pdf":
 
 
<haskell>
 
import Graphics.PDF
 
 
main :: IO ()
 
main = do
 
let outputFileName= "test1.pdf"
 
let defaultPageSize = PDFRect 0 0 200 300
 
 
runPdf outputFileName standardDocInfo defaultPageSize $ do
 
addPage Nothing
 
</haskell>
 
 
=== Pages with different sizes ===
 
 
If you pass "Nothing" to the function [http://hackage.haskell.org/packages/archive/HPDF/latest/doc/html/Graphics-PDF-Document.html#v%3AaddPage addPage], the default page size will be used for the size of the new page.
 
 
Let’s create three pages, the last two pages with different dimensions:
 
 
<haskell>
 
import Graphics.PDF
 
 
main :: IO ()
 
main = do
 
let outputFileName= "test2.pdf"
 
let defaultPageSize = PDFRect 0 0 200 300
 
 
runPdf outputFileName standardDocInfo defaultPageSize $ do
 
addPage Nothing
 
addPage $ Just $ PDFRect 0 0 100 100
 
addPage $ Just $ PDFRect 0 0 150 150
 
</haskell>
 
 
== FFI ==
 
=== How to interface with C===
 
 
Magnus has written [http://therning.org/magnus/archives/315 a nice example ] on how to call a C function operating on a user defined type.
 
 
== Testing ==
 
 
=== QuickCheck ===
 
 
TODO
 
 
=== HUnit ===
 
 
TODO
 

Latest revision as of 18:49, 26 May 2011

[edit] 1 Haskell Cookbook

[edit] 2 Similar projects for other programming languages