Comment (computer programming): Difference between revisions

Revision as of 14:13, 11 January 2025

Revision as of 14:23, 11 January 2025

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</syntaxhighlight>

===By=Double languagedash====

A relatively loose collection of languages use <code>--</code> for a single line comment. Notable languages include: [[Ada (programming language)|Ada]] and [[Haskell]]. An example in Ada:

====Ada====

[[Ada (programming language)|Ada]] supports line comments delimited with '--'. It does not support block comments. For example:

<syntaxhighlight lang="ada">

-- the air traffic controller task takes requests for takeoff and landing

task type Controller (My_Runway: Runway_Access) is

-- task entries for synchronous message passing

entry Request_Takeoff (ID: in Airplane_ID; Takeoff: out Runway_Access);

entry Request_Approach(ID: in Airplane_ID; Approach: out Runway_Access);

end Controller;

</syntaxhighlight>

====Block in Haskell====

In Haskell, a block comment is delimited by <code>{-</code> and <code>-}</code>. For example:

<syntaxhighlight lang="Haskell">

{- this is a comment

on more lines -}

-- and this is a comment on one line

putStrLn "Wikipedia" -- this is another comment

</syntaxhighlight>

Haskell also provides a [[literate programming]] method of commenting known as "Bird Style".<ref>{{cite web |url=http://www.haskell.org/haskellwiki/Literate_programming#Bird_Style |title=Literate programming |website=haskell.org}}</ref> In this all linesLines starting with <code>></code> are interpreted as code, and everything else is considered a comment. One additional requirement is that you always leave a blank line before and after the code block:

<syntaxhighlight lang="lHaskell">

In Bird-style you have to leave a blank before the code.

> fact :: Integer -> Integer

> fact 0 = 1

> fact (n+1) = (n+1) * fact n

And you have to leave a blank line after the code as well.

</syntaxhighlight>

Literate programming can also be accomplished via [[LaTeX]]. Example of a definition:

<syntaxhighlight lang="lHaskell">

\usepackage{verbatim}

\newenvironment{code}{\verbatim}{\endverbatim}

</syntaxhighlight>

Used as follows:

<syntaxhighlight lang="lhaskell">

% the LaTeX source file

The \verb|fact n| function call computes $n!$ if $n\ge 0$, here is a definition:\\

\begin{code}

fact :: Integer -> Integer

fact 0 = 1

fact (n+1) = (n+1) * fact n

\end{code}

Here more explanation using \LaTeX{} markup

</syntaxhighlight>

===By language===

====APL====

Line 596 ⟶ 637:

print '(A)', 'Hello world' ! Fortran 90 introduced the option for inline comments.

end program

</syntaxhighlight>

====Haskell====

Line comments in Haskell start with '--' (two hyphens) until the end of line, and multiple line comments start with '{-' and end with '-}'.

<syntaxhighlight lang="Haskell">

{- this is a comment

on more lines -}

-- and this is a comment on one line

putStrLn "Wikipedia" -- this is another comment

</syntaxhighlight>

Haskell also provides a [[literate programming]] method of commenting known as "Bird Style".<ref>{{cite web |url=http://www.haskell.org/haskellwiki/Literate_programming#Bird_Style |title=Literate programming |website=haskell.org}}</ref> In this all lines starting with > are interpreted as code, everything else is considered a comment. One additional requirement is that you always leave a blank line before and after the code block:

<syntaxhighlight lang="lHaskell">

In Bird-style you have to leave a blank before the code.

> fact :: Integer -> Integer

> fact 0 = 1

> fact (n+1) = (n+1) * fact n

And you have to leave a blank line after the code as well.

</syntaxhighlight>

Literate programming can also be done in Haskell, using [[LaTeX]]. The code environment can be used instead of the Richard Bird's style:

In [[LaTeX]] style this is equivalent to the above example, the code environment could be defined in the LaTeX preamble. Here is a simple definition:

<syntaxhighlight lang="lHaskell">

\usepackage{verbatim}

\newenvironment{code}{\verbatim}{\endverbatim}

</syntaxhighlight>

later in

<syntaxhighlight lang="lhaskell">

% the LaTeX source file

The \verb|fact n| function call computes $n!$ if $n\ge 0$, here is a definition:\\

\begin{code}

fact :: Integer -> Integer

fact 0 = 1

fact (n+1) = (n+1) * fact n

\end{code}

Here more explanation using \LaTeX{} markup

</syntaxhighlight>