Difference between revisions of "User:Lenny222/Haskell explained to the busy"

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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 [http://en.wikipedia.org/wiki/Haskell_Curry Haskell Curry]
 
 
== Basics ==
 
{| class="wikitable"
 
|-
 
! Question
 
! Answer
 
|-
 
|What is an '''infix operator'''?
 
| Infix operators are normal functions. TODO: symbols, round brackets
 
For example:
 
<haskell>5 + 2</haskell>
 
is the same as
 
<haskell>(+) 5 2</haskell>
 
|-
 
|Are there any '''prefix operators'''?
 
|TODO
 
|-
 
|How do you '''define a function''' in Haskell?
 
| TODO
 
For example:
 
<haskell>add x y = x + y</haskell>
 
|-
 
|Didn't you say Haskell is statically typed?
 
| It is. TODO
 
|-
 
|What is '''point-free style'''?
 
|Point-free style is a way to define functions solely as a composition of other functions, leaving out arguments in the definition.
 
For example:
 
<haskell>takeFive x = take 5 x</haskell>
 
is the same as
 
<haskell>takeFive = take 5</haskell>
 
in point-free style.
 
|-
 
|What is '''currying'''?
 
| TODO
 
|-
 
|What is '''pattern matching'''?
 
| TODO
 
 
|}
 
 
== Advanced ==
 
 
{| class="wikitable"
 
|-
 
! Question
 
! Answer
 
|-
 
|What is a '''Monad'''?
 
|TODO
 
|-
 
|What is the meaning of "'''forall'''"?
 
|TODO
 
|}
 
 
== Special characters, expressions and keywords ==
 
 
=== . ===
 
The dot "." is used to compose functions in point-free style, similar to "$".
 
 
Example:
 
<haskell>foo x = h $ g $ f x</haskell>
 
is the same as
 
<haskell>foo = h . g . f</haskell>
 
 
=== ` ===
 
A function enclosed in back ticks "`"s can be used as an infix operator.
 
 
Example:
 
<haskell>subtract 2 10</haskell>
 
is the same as
 
<haskell>2 `subtract` 10</haskell>
 
 
=== ' ===
 
Backtick TODO: single characters, common usage in function names
 
 
=== : ===
 
The colon ":" is an infix operator that adds an element to the beginning of a list
 
 
Example:
 
<haskell>1 : [2,3]</haskell>
 
will result in the new list
 
<haskell>[1,2,3]</haskell>
 
 
=== :: ===
 
The double colon TODO
 
 
=== | ===
 
Downslash TODO: pattern matching, data types
 
 
=== \ ===
 
Backslash
 
TODO: multiline strings, lambda function
 
 
=== $ ===
 
The dollar sign "$" is a way to compose functions, but avoid typing too many brackets.
 
 
Example:
 
<haskell>foo x = h (g (f x))</haskell>
 
is the same as
 
<haskell>foo x = h $ g $ f x</haskell>
 
 
=== -- ===
 
The double dash "-- " (a trailing space is necessary) begins a '''single-line comment'''. The rest of the line will be ignored by the compiler.
 
 
Example:
 
<haskell>-- Sort the list
 
sort [3,2,4]
 
</haskell>
 
or
 
<haskell>sort [3,2,4] -- Sort the list</haskell>
 
 
=== [ ] ===
 
The square brackets TODO
 
 
=== {- -} ===
 
 
{| class="wikitable"
 
|-
 
! Meaning
 
! Example
 
|-
 
|Everything between "{- " and "-}" is a '''block comment''' and will be ignored by the compiler.
 
 
Note that the space after "{- " is necessary.
 
|<haskell>
 
{-
 
The next line would sort the list, if it wasn't in a block comment
 
sort [3,2,4]
 
-}
 
</haskell>
 
|}
 
 
=== {-# #-} ===
 
"{-# " (the trailing space is necessay) and "#-}" define '''compiler pragmas'''. TODO
 
 
=== data ===
 
"data" defines a new data type. TODO
 
 
Example:
 
<haskell>data colors = Red | Blue | Green</haskell>
 
 
=== deriving ===
 
TODO
 
 
=== newtype ===
 
TODO
 
 
=== type ===
 
TODO
 

Latest revision as of 15:52, 19 February 2010