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Revision as of 13:49, 1 October 2009
You have heard about Haskell but don't have the time to find out what it is?
This page may be for you.
Introduction
What is Haskell?
Haskell is a purely functional, lazy, statically typed programming language
What is a purely functional programming language?
What is good about that?
What is lazy evaluation?
What is good about that?
What is static typing?
What is good about that?
Is Haskell Open Source?
Why the name "Haskell"?
Haskell is named after the American mathematician Haskell Curry
Functions
How do i apply functions?
TODO
What is the "Prelude"?
The Prelude is a standard module that is available to all Haskell code by default.
What is currying?
TODO
How do i define a function?
TODO
Answer | Example |
---|---|
TODO | add x y = x + y
|
Didn't you say Haskell is statically typed? It is. TODO
What is an infix operator?
Answer | Example |
---|---|
Infix operators are normal functions.
TODO: symbols, round brackets |
5 + 2
is the same as (+) 5 2
|
Are there any prefix operators?
TODO: (-)
What is point-free style?
Answer | Example |
---|---|
Point-free style is a way to define functions solely as a composition of other functions.
Function arguments do not show up in the function definition. |
The point-free style version of
takeFive x = take 5 x
is takeFive = take 5
|
What is a higher-order function?
TODO
What is pattern matching?
TODO
Data types
TODO
Lists
TODO
Strings
TODO
Tupels
TODO
Tuples
Defining your own types
Type classes
What is a type variable?
TODO
What is a type class?
TODO
Comments
How do i write single-line comments?
Answer | Example |
---|---|
Everything between a double dash "--" followed by a space and the end of the line is a single-line comment.
A single-line comment will be ignored by the compiler. |
-- Sort the list
sort [3,2,4]
or sort [3,2,4] -- Sort the list
|
How do i write block comments?
Answer | Examples |
---|---|
Everything between "{-" followed by a space and "-}" is a block comment.
A block comment will be ignored by the compiler. |
{-
The next line would sort the list, if it wasn't in a block comment
sort [3,2,4]
-}
or sort [3,2,4] {- Block quotes can also be used for single line comments -}
|
Special characters, expressions and keywords
.
Meaning | Example |
---|---|
The dot "." is used to compose functions in point-free style, similar to "$". | foo = h . g . f
is the same as foo x = h $ g $ f x
which is the same as foo x = h (g (f x))
|
`
Meaning | Example |
---|---|
A function enclosed in back ticks "`" can be used as an infix operator. | 2 `subtract` 10
is the same as subtract 2 10
|
'
Tick TODO: single characters, common usage in function names
:
Meaning | Example |
---|---|
The colon ":" is an infix operator that adds an element to the beginning of a list. | 1 : [2,3]
will result in the new list [1,2,3]
|
::
The double colon TODO
|
Downslash TODO: pattern matching, data types
\
Backslash TODO: multiline strings, lambda function
$
Meaning | Example |
---|---|
The dollar sign "$" is a way to compose functions, without typing too many brackets. | foo x = h $ g $ f x
is the same as foo x = h (g (f x))
|
--
Meaning | Example |
---|---|
The double dash "--" followed by a space begins a single-line comment. | -- A single-line comment
|
[ ]
The square brackets TODO
{- -}
Meaning | Example |
---|---|
Everything between "{-" followed by a space and "-}" is a block comment. | {-
This is a block comment
-}
|
{-# #-}
"{-# " (the trailing space is necessay) and "#-}" define compiler pragmas. TODO
data
Meaning | Example |
---|---|
"data" defines a new data type. TODO |
data colors = Red | Blue | Green
|
deriving
TODO
forall
TODO
newtype
TODO
type
TODO