Revision as of 10:40, 23 April 2009
- Dates and time
- Other data structures
- Pattern matching
- Network programming
- Databases access
- Graphical user interfaces
- PDF files
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
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
3.1 How to interface with C
Magnus has written a nice example on how to call a C function operating on a user defined type.