Cookbook
- Strings
- Numbers
- Dates and time
- Lists
- Other data structures
- Pattern matching
- Interactivity
- Files
- Network programming
- XML
- Databases access
- Graphical user interfaces
This article is a draft, with further revisions actively invited. Drafts are typically different than stubs in that these articles are in an active edit process. Feel free to help by expanding the article.
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
Prelude
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.
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>
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
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
PDF files
For the following recipes you need to install HPDF.
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
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
FFI
How to interface with C
Magnus has written a nice example on how to call a C function operating on a user defined type.
Testing
QuickCheck
TODO
HUnit
TODO