Editing Programming style (section)

===== Haskell =====
[[Haskell]], like Python, has the ''off-side rule''. It has a two-dimension syntax where indenting is meaningful to define blocks (although, an alternate syntax uses curly braces and semicolons).

Haskell is a declarative language, there are statements, but declarations within a Haskell script.

Example:

<syntaxhighlight lang="haskell">
let c_1 = 1
    c_2 = 2
in
    f x y = c_1 * x + c_2 * y
</syntaxhighlight>
may be written in one line as:
<syntaxhighlight lang="haskell">
let {c_1=1;c_2=2} 
in f x y = c_1 * x + c_2 * y
</syntaxhighlight>
Haskell encourages the use of [[literate programming]], where extended text explains the genesis of the code. In literate Haskell scripts (named with the <code>lhs</code> extension), everything is a comment except blocks marked as code. The program can be written in [[LaTeX]], in such case the <code>code</code> environment marks what is code. Also, each active code paragraph can be marked by preceding and ending it with an empty line, and starting each line of code with a greater than sign and a space. Here an example using LaTeX markup:
<syntaxhighlight lang="haskell">
The function \verb+isValidDate+ test if date is valid
\begin{code}
isValidDate :: Date -> Bool
isValidDate date = hh>=0  && mm>=0 && ss>=0
                 && hh<24 && mm<60 && ss<60
 where (hh,mm,ss) = fromDate date
\end{code}
observe that in this case the overloaded function is \verb+fromDate :: Date -> (Int,Int,Int)+.
</syntaxhighlight>

And an example using plain text:
<syntaxhighlight lang="haskell">
The function isValidDate test if date is valid

> isValidDate :: Date -> Bool
> isValidDate date = hh>=0  && mm>=0 && ss>=0
>                  && hh<24 && mm<60 && ss<60
>  where (hh,mm,ss) = fromDate date

observe that in this case the overloaded function is fromDate :: Date -> (Int,Int,Int).
</syntaxhighlight>