Revision as of 10:38, 23 April 2009
- Dates and time
- Other data structures
- Pattern matching
- Network programming
- Databases access
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We need to start a Haskell centered cookbook (aka, not a PLEAC clone)
This page is based on the Scheme Cookbook at http://schemecookbook.org/Cookbook/WebHome
A lot of functions are defined in the "Prelude". Also, if you ever want to search for a function, based on the name, type or module, take a look at the excellent Hoogle. This is for a lot of people a must-have while debugging and writing Haskell programs.
2.1 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>
Prelude is the "base" library of Haskell.
To create variables at the GHCi prompt, use `let'
Prelude> let x = 5 Prelude> x 5 Prelude> let y = 3 Prelude> y 3 Prelude> x + y 8
`let' is also the way to create simple functions at the GHCi prompt
Prelude> let fact n = product [1..n] Prelude> fact 5 120
2.2 Checking Types
To check the type of an expression or function, use the command `:t'
Prelude> :t x x :: Integer Prelude> :t "Hello" "Hello" :: [Char]
Haskell has the following types defined in the Standard Prelude.
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
3 Graphical user interfaces
wxHaskell is a portable and native GUI library for Haskell based on the wxWidgets Library.
Hello World example:
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]
This code was taken from "a quick start with wxHaskell".
Hello world example:
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
For more examples, see: Applications and libraries/Games
See also: Applications and libraries/Games
4 PDF files
For the following recipes you need to install HPDF.
4.1 Creating an empty PDF file
The following code creates an empty PDF file with the name "test1.pdf":
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
4.2 Pages with different sizes
If you pass "Nothing" to the function 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:
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
5.1 How to interface with C
Magnus has written a nice example on how to call a C function operating on a user defined type.