Difference between revisions of "Cookbook/Compilers and interpreters"
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| − | A lot of functions are defined in the [[Prelude]]. The Prelude is a standard module imported by default into all Haskell module. |
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| − | 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. |
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| − | == GHCi interaction == |
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| − | To start GHCi from a command prompt, simply type `ghci' |
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| − | $ ghci |
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| − | ___ ___ _ |
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| − | / _ \ /\ /\/ __(_) |
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| − | / /_\// /_/ / / | | GHC Interactive, version 6.6, for Haskell 98. |
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| − | / /_\\/ __ / /___| | http://www.haskell.org/ghc/ |
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| − | \____/\/ /_/\____/|_| Type :? for help. |
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| − | Loading package base ... linking ... done. |
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| − | Prelude> |
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| − | [[Prelude]] is the "base" library of Haskell. |
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| − | To create variables at the GHCi prompt, use `let' |
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| − | <haskell> |
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| − | Prelude> let x = 5 |
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| − | Prelude> x |
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| − | 5 |
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| − | Prelude> let y = 3 |
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| − | Prelude> y |
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| − | 3 |
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| − | Prelude> x + y |
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| − | 8 |
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| − | </haskell> |
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| − | `let' is also the way to create simple functions at the GHCi prompt |
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| − | <haskell> |
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| − | Prelude> let fact n = product [1..n] |
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| − | Prelude> fact 5 |
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| − | 120 |
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| − | </haskell> |
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== Checking Types == |
== Checking Types == |
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Revision as of 08:11, 31 August 2009
GHC
GHCi
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