Difference between revisions of "Cookbook"
Jump to navigation
Jump to search
(Added link to similar F# cookbook) |
|||
| (37 intermediate revisions by one other user not shown) | |||
| Line 1: | Line 1: | ||
| + | == Haskell Cookbook == |
||
| − | [[Category:How to]] |
||
| + | * [[Cookbook/Compilers and interpreters|Haskell compilers and interpreters]] |
||
| − | |||
| − | * [[Cookbook/Strings|Strings]] |
||
* [[Cookbook/Numbers|Numbers]] |
* [[Cookbook/Numbers|Numbers]] |
||
| + | * [[Cookbook/Lists and strings|Lists and strings]] |
||
| + | * [[Cookbook/Other data structures|Other data structures]] |
||
* [[Cookbook/Dates And Time|Dates and time]] |
* [[Cookbook/Dates And Time|Dates and time]] |
||
| − | * [[Cookbook/ |
+ | * [[Cookbook/Pattern matching|Pattern matching]] |
| + | * [[Cookbook/Interactivity|Interactivity]] |
||
| + | * [[Cookbook/Files|Files]] |
||
| + | * [[Cookbook/Network programming|Network programming]] |
||
| + | * [[Cookbook/XML|XML]] |
||
| + | * [[Cookbook/Databases access|Databases access]] |
||
| + | * [[Cookbook/Graphical user interfaces|Graphical user interfaces]] |
||
| + | * [[Cookbook/PDF files|PDF files]] |
||
| + | * [[Cookbook/FFI|FFI]] |
||
| + | * [[Cookbook/Testing|Testing]] |
||
| + | == Similar projects for other programming languages == |
||
| − | {{Template:Anonymousdraft}} |
||
| + | * [http://cl-cookbook.sourceforge.net/ Common Lisp Cookbook] |
||
| − | |||
| − | + | * [http://pleac.sourceforge.net/ PLEAC] |
|
| + | * [http://www.zenspider.com/Languages/Ruby/Cookbook/index.html Ruby Cookbook] |
||
| − | |||
| − | + | * [http://schemecookbook.org/Cookbook/WebHome Scheme Cookbook] |
|
| + | * [http://fssnip.net/ F# Snippets] |
||
| − | http://schemecookbook.org/Cookbook/WebHome''' |
||
| + | [[Category:FAQ]] |
||
| − | == Prelude == |
||
| + | [[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> |
||
| − | |||
| − | |||
| − | |||
| − | |||
| − | |||
| − | == Pattern matching == |
||
| − | |||
| − | Regular expressions are useful in some situations where the Data.List |
||
| − | library is unwieldy. Posix style regular expressions are available in |
||
| − | the core libraries, and a suite of other regular expression libraries |
||
| − | are [also available], including PCRE and TRE-style regexes. |
||
| − | |||
| − | Bryan O'Sullivan has written [http://www.serpentine.com/blog/2007/02/27/a-haskell-regular-expression-tutorial/ a nice introduction] to using the new regex libraries. |
||
| − | |||
| − | == Interactivity == |
||
| − | |||
| − | === Reading a string === |
||
| − | Strings can be read as input using [http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v%3AgetLine getLine]. |
||
| − | <haskell> |
||
| − | Prelude> getLine |
||
| − | Foo bar baz |
||
| − | "Foo bar baz" |
||
| − | </haskell> |
||
| − | |||
| − | === Printing a string === |
||
| − | Strings can be output in a number of different ways. |
||
| − | <haskell> |
||
| − | Prelude> putStr "Foo" |
||
| − | FooPrelude> |
||
| − | </haskell> |
||
| − | As you can see, [http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v%3AputStr putStr] does not include the newline character `\n'. We can either use putStr like this: |
||
| − | <haskell> |
||
| − | Prelude> putStr "Foo\n" |
||
| − | Foo |
||
| − | </haskell> |
||
| − | Or use [http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v%3AputStrLn putStrLn], which is already in the Standard Prelude |
||
| − | <haskell> |
||
| − | Prelude> putStrLn "Foo" |
||
| − | Foo |
||
| − | </haskell> |
||
| − | We can also use [http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v%3Aprint print] to print a string, '''including the quotation marks.''' |
||
| − | <haskell> |
||
| − | Prelude> print "Foo" |
||
| − | "Foo" |
||
| − | </haskell> |
||
| − | |||
| − | === Parsing command line arguments === |
||
| − | |||
| − | TODO |
||
| − | |||
| − | == Files == |
||
| − | |||
| − | === Reading from a file === |
||
| − | The System.IO library contains the functions needed for file IO. The program |
||
| − | below displays the contents of the file c:\test.txt. |
||
| − | |||
| − | <haskell> |
||
| − | import System.IO |
||
| − | |||
| − | main = do |
||
| − | h <- openFile "c:\\test.txt" ReadMode |
||
| − | contents <- hGetContents h |
||
| − | putStrLn contents |
||
| − | hClose h |
||
| − | </haskell> |
||
| − | |||
| − | The same program, with some higher-lever functions: |
||
| − | |||
| − | <haskell> |
||
| − | main = do |
||
| − | contents <- readFile "c:\\test.txt" |
||
| − | putStrLn contents |
||
| − | </haskell> |
||
| − | |||
| − | === Writing to a file === |
||
| − | |||
| − | The following program writes the first 100 squares to a file: |
||
| − | <haskell> |
||
| − | -- generate a list of squares with length 'num' in string-format. |
||
| − | numbers num = unlines $ take num $ map (show . \x -> x*x) [1..] |
||
| − | |||
| − | main = do |
||
| − | writeFile "test.txt" (numbers 100) |
||
| − | putStrLn "successfully written" |
||
| − | </haskell> |
||
| − | |||
| − | This will override the old contents of the file, or create a new file if the file doesn't exist yet. If you want to append to a file, you can use <hask>appendFile</hask>. |
||
| − | |||
| − | === Creating a temporary file === |
||
| − | |||
| − | TODO |
||
| − | |||
| − | === Writing a filter === |
||
| − | Using [http://haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:interact interact], you can easily do things with stdin and stdout. |
||
| − | |||
| − | A program to sum up numbers: |
||
| − | |||
| − | <haskell>main = interact $ show . sum . map read . lines</haskell> |
||
| − | |||
| − | A program that adds line numbers to each line: |
||
| − | |||
| − | <haskell> |
||
| − | main = interact numberLines |
||
| − | numberLines = unlines . zipWith combine [1..] . lines |
||
| − | where combine lineNumber text = concat [show lineNumber, " ", text] |
||
| − | </haskell> |
||
| − | |||
| − | === Logging to a file === |
||
| − | |||
| − | TODO |
||
| − | |||
| − | == 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
Haskell Cookbook
- Haskell compilers and interpreters
- Numbers
- Lists and strings
- Other data structures
- Dates and time
- Pattern matching
- Interactivity
- Files
- Network programming
- XML
- Databases access
- Graphical user interfaces
- PDF files
- FFI
- Testing