Cookbook/Compilers and interpreters
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Revision as of 23:24, 22 July 2009 by HowardBGolden (talk | contribs) (Change more Prelude links to HaskellWiki page)
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Prelude
A lot of functions are defined in the Prelude. The Prelude is a standard module imported by default into all Haskell module.
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 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