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Task

Show all ways to include text in a language source file that's completely ignored by the compiler or interpreter.

Related tasks

See also

Wikipedia
xkcd (Humor: hand gesture denoting // for "commenting out" people.)

11l

// Single line comment
\\ Also single line comment (continuation of the comment in previous line)

\[ This is
a multi line
comment ]

\{ And
this }

\( And
this )

\‘ And
this ’

360 Assembly

* An asterisk in column one denotes a comment line
* Comments may also follow any syntactically complete instruction: 
         LA    1,0           Comment 
         NOP                 Comment (after a NOP instruction)
* Comments after instructions with omitted operands require a comma ","
         END   ,             Comment (without comma, "Comment" assumed an operand of "END")

4D

`Comments in 4th Dimension begin with the accent character and extend to the end of the line (until 4D version 2004).
// This is a comment starting from 4D v11 and newer. Accent character is replaced by //

4ME

P:This is a comment
out{hi!} This i also a comment
# This is a Python-Like comment
E:
Anything after the "E:" command wont be executed

6502 Assembly

Note: syntax depends on the assembler software but use of a semicolon is fairly standard

          nop           ; comments begin with a semicolon

68000 Assembly

Note: syntax depends on the assembler software but use of a semicolon is fairly standard

EASy68k uses * as the comment character. VASM uses a semicolon ;

            MOVEM.L D0-D7/A0-A6,-(SP)  ;push all registers onto the stack

8086 Assembly

Note: syntax depends on the assembler software but use of a semicolon is fairly standard

	MOV AX, 4C00h 		; go back to DOS
	INT 21h                 ; BIOS interrupt 21 base 16

AArch64 Assembly

Works with: as version Raspberry Pi 3B version Buster 64 bits

/* ARM assembly AARCH64 Raspberry PI 3B */
/*  comments multi lines

    end comments
    */

               // comment end of ligne

ACL2

Just like Common Lisp:

; Single line comment
#| Multi-line
comment |#

Action!

Action! supports only single line comments which begin with semicolon.

;This is a comment

PROC Main() ;This is a comment as well
RETURN

Output:

Screenshot from Atari 8-bit computer

Ada

-- All Ada comments begin with "--" and extend to the end of the line

Agena

Agena has single line comments and two styles of multi-line comments.

# single line comment

#/ multi-line comment
   - ends with the "/ followed by #" terminator on the next line
/#

/* multi-line comment - C-style
   - ends with the "* followed by /" terminator on the next line
*/

ALGOL 60

A comment in ALGOL 60 takes the place of a single instruction.

'COMMENT' this is a first comment;
'COMMENT' 
****** this is a second comment ******
;

ALGOL 68

With Standard

Comments can be inserted in variety of ways:

Algol68 as typically published, includes bold typeface.	Quote stropping, like to Wiki markup.	Case stropping, 7-bit/ascii implementations.	Res stropping, detecting reserved words.	Point stropping, 6-bits/byte implementations.
¢ The original way of adding your 2 cents worth to a program with the "cent" character ¢				¢ TEXT ¢
co Style i comment co comment text comment	'co' text 'co' 'comment' text 'comment'	CO text CO COMMENT text COMMENT	co text co comment text comment	.CO TEXT .CO .COMMENT TEXT .COMMENT
# Style ii comment with the hash character #				# TEXT #

Notes:

The # test # and ¢ text ¢ comment tends to be used for inline comments. And the COMMENT text COMMENT style tends to be used to comment out entire blocks.
The script algol68.vim can be used to highlight commented blocks while editing source code.

With Extensions

£ This is a hash/pound comment for a UK keyboard £

ALGOL-M

begin

comment - This form is borrowed from ALGOL 60;

% And this is borrowed from ALGOL W %

% ALGOL-M will not compile an "empty" program, so we have %
% to include at least one code-generating statement!      %
write("This is only an exercise");

end

Comments in Algol W can appear anywhere whitespace is allowed. A comment starts with the reserved word 'comment' and ends with the next semi-colon. Alternatively a comment can start with a percent sign and end with the next percent sign or semi-colon.

A single word in the form of an identifier following the reserved word 'end' is also a comment.

begin
    comment a comment;
    % another comment
    ;
    % and
      another
    %
end this_word_is_also_a_comment.

AmigaE

/* multiline comment
are like C ... */
-> this is a end of line comment

AngelScript

// This is a comment

AntLang

2 + 2 /This is a comment

Apex

System.debug ('I will execute');   // This comment is ignored.
/*
 I am a large comment, completely ignored as well.
*/

APL

⍝ This is a comment

AppleScript

--This is a single line comment

display dialog "ok" --it can go at the end of a line

# Hash style comments are also supported

(* This is a multi
line comment*)

(* This is a comment. --comments can be nested
  (* Nested block comment *)
*)

Works with: AppleScript version 2.0

display dialog "ok" #Starting in version 2.0, end-line comments can begin with a hash

Arendelle

Arendelle uses C style comments

ARM Assembly

Works with: as version Raspberry Pi

/* ARM assembly Raspberry PI comment one line */
/*  comment line 1
    comment line 2
*/ 

	mov r0,#0    @ this comment on end of line
	mov r1,#0    //  authorized comment

Arturo

; This is a simple single-line comment

a: 10 ; another single-line comment

; Now, this is a
; multi-line comment

Asymptote

// double slash to newline

See programming introduction in the Asymptote manual.

When reading data files a comment character in them can be specified as comment="#" etc. See Files in the Asymptote manual.

AutoHotkey

Msgbox, comments demo ; end of line comment
/*
multiline comment1
multiline comment2
*/

For multi-line comments, the /* and */ must be on their own separate lines. Nothing else can be on the same line.

AutoIt

#cs
Everything between the cs and and the ce is commented.
Commented code is not used by the computer.
#ce
;individual lines after a semicolon are commented.

AWK

The hash symbol # start a comment; it ends at the end of line.

BEGIN { # this code does something
  # do something
}

Axe

.This is a single-line comment

...
This is a multi-line comment
...

...If 0
This is a comment only if the condition evaluates to zero
...

...!If 1
This is a comment only if the condition evaluates to nonzero
...

...Else
This is a comment only if the previous conditional comment was executed (and vice versa)
...

Babel

-- This is a line-comment

#
    This is a block-comment
    It goes until de-dent

dedent: 0x42 -- The comment block above is now closed

BASIC

Works with: Applesoft BASIC

Works with: Commodore BASIC

Works with: GW-BASIC

Works with: ZX Spectrum Basic

Works with: uBasic/4tH

The only truly standard method of marking a comment in BASIC is using the REM keyword. This dates back to (at least) the late 1970's, and should work with most BASICs available today:

100 REM Standard BASIC comments begin with "REM" (remark) and extend to the end of the line
110 PRINT "this is code": REM comment after statement

Works with: Applesoft BASIC

This may not be well known, but you may include text after the line number of GOTO and GOSUB statements. This is kind of a comment in absence of labels.

100  GOTO 200HERE                      
110  GOSUB 300THERE                    
120  GOTO 400THEOTHERPLACE             
130  GOTO 500MOM AND  POP

Spaces are removed from non-keyword text. BASIC keywords can be used. List outputs spaces around keywords.

Works with: QBasic version 1.1

Works with: QuickBASIC version 4.5

Works with: uBasic/4tH

Most BASICs also support alternate comment characters, commonly an apostrophe (single quote):

 'this is a comment
 PRINT "this is code"  'comment after statement

Works with: DarkBASIC

Characters other than apostrophe are used in some BASICs. For example, DarkBASIC uses a back-tick character (`, a.k.a. grave accent):

`this is a comment
PRINT "this is code" `comment after statement
'this is NOT a comment!

Works with: FreeBASIC version 0.16 or later

In addition to single-line comments, a few BASICs support block comments. FreeBASIC was influenced by the C family's block comment characters:

/' This is a multi line comment.
Requires FreeBASIC 0.16 or later.
Last line of the comment block. '/

DIM a AS /' Comment in the middle of statement '/ Integer

Applesoft BASIC

Comment by making a REMark using the REM keyword

REM COMMENT AFTER THE REM KEYWORD

When LISTing the program a space is added after the REM keyword

0  REMLEAVE THE SPACE OUT AFTER THE REM WHEN TYPING OR PASTING

The remark extends until the end of the line. Only the first THIS IS CODE is printed.

10  PRINT "THIS IS CODE" : REM : PRINT "THIS IS CODE"

A comment can come after a GOSUB and when the subroutine returns it continues running the statements after the GOSUB comment.

20  GOSUB 110COMMENT: PRINT "THIS IS CODE"

Anything after a GOTO or RETURN statement is ignored.

30  GOTO 40"COMMENT: THIS IS A COMMENT

There are other ways to add spacing and comments to code.

::::::::::::::::::::::::::::::::::::::
40  REM
50  :
60  REM<ctrl>+J

70  FOR I = 1 to 10
80  ::::PRINT I;MID$("THIS IS A COMMENT",1,0)
90  NEXT

Typing CONTinue after the program ENDs will result in a ?SYNTAX ERROR.

100 END : THISISACOMMENT

Use the quotation symbol " before the comment so that spaces are included and keywords are ignored.

110 RETURN : "COMMENT FOR AND AT THE END

BaCon

BaCon accepts REM (or single quote apostrophe) for line comments.

C-style block comments can be used with /* and */ pairs; these comment blocks may cross line boundaries.

Inside USEC sections, all comment styles accepted by the configured C compiler will also be ignored.

BASIC256

rem this is a comment
# and this is too
print "this is code"  #comment after statement

Chipmunk Basic

Works with: Chipmunk Basic version 3.6.4

10 rem this is a comment
20 ' and this is too
30 print "this is code" : 'comment after statement
40 print "and more code" : rem comment after statement

IS-BASIC

100 REM Standard BASIC comments begin with "REM" (remark) and extend to the end of the line
110 PRINT "this is code" ! comment after statement

Minimal BASIC

10 REM STANDARD BASIC COMMENTS BEGIN WITH "REM" AND EXTEND TO THE END OF LINE
20 END

MSX Basic

10 rem this is a comment
20 ' and this is too
30 print "this is code" : '[:] it's optional
40 print "and more code" : rem comment after statement

Quite BASIC

10 rem this is a comment
20 print "this is code" : rem comment after statement

True BASIC

!this is a comment
 PRINT "this is code"  !comment after statement

XBasic

Works with: Windows XBasic

Works with: Linux XBasic

PROGRAM  "Comments"
VERSION  "0.0000"

DECLARE FUNCTION Entry ()

FUNCTION  Entry ()
	'this is a comment
	PRINT "this is code"  'comment after statement
END FUNCTION
END PROGRAM

Yabasic

rem  Hey, this is a comment
#    the hash-sign too (at beginning of line)
// even the double slash
' and the single quote (at beginning of line)
print "Not a comment" #    This is an error !!
print "Not a comment"://   But this is again a valid comment
print "Not a comment" //   even this.
print "Not a comment" rem  and this !

Batch File

rem Single-line comment.

There is another (undocumented) option, using a double-colon ::. However, this has issues with some syntactic constructs and therefore may raise syntax errors.

:: Another option, though undocumented and known
:: to fail in some cases. Best avoided.

Yet another (undocumented) option, using (not delayed) variable expansion as long as it is undefined. This works because undefined variables result to blank line when expanded using %.

% this works as long as you have no variable named exactly like this sentence. %

Since comment lines are skipped entirely by the parser, multi-line comments aren't possible even with line continuation.

BBC BASIC

      REM This is a comment which is ignored by the compiler
      *| This is a comment which is compiled but ignored at run time

bc

/* This is a comment. */

2 + /* Comment between tokens. */ 3

"This is a string, /* NOT a comment */."

/*
 * A comment can have multiple lines. These asterisks in the middle
 * of the comment are only for style. You must not nest a comment
 * inside another comment; the first asterisk-slash ends the comment.
 */

Works with: GNU bc

Works with: OpenBSD bc

#!/usr/bin/bc

# This form of comment is an extension, not part of standard bc.

# Your program must not have a #! shebang line
# unless your bc supports this form of comment.

2 + 3  # It can be after a statement.

a = 1  # The newline is not part of the comment.
b = 2  # So this line is a different statement.

Beef

//This is a comment.
//This is another comment.

/* This is also a comment. */

/* This is a 
multi-line
comment */

The IDE allows for documenting types and methods with /// or /** */ (which one of these you use doesn’t matter). Autocomplete suggestions, as well as prompts while calling/using the documented types or functions, will display their documentation.

static
{
    /// Must be placed directly above the method, including attributes.
    /// Using multiple lines like this is also fine. Both will be recognized.
    [Optimize]
    public static void DoAThing() {}

    /// Documentation also works for types.
    struct SomeStruct
    {
        /**
        * Multiline comment with two ** at the start works in the same way.
        */
        void PrivateMethod() {}
    }

    /**
    * If you have a really long explainer here, you may not actually want to show that in autcompletion prompts.
    * @brief Allows you to select only this line to be shown.
    * 
    * @param a This is shown when writing a call to this function and placing parameter "a".
    * @param b For the second argument, the documentation for b (this!) will show up instead.
    */
    public static void DoAnotherThing(int a, int b) {}
}

Befunge

Like Brainf***, all characters and whitespace which are not commands are ignored. Also, since the code/data-space is two-dimensional, comments can be placed anywhere that will be untouched by the instruction pointer and data access commands. Finally, in Funge-98, the ; instruction immediately skips to the next ; instruction, which allows to isolate comments from code.

Works with: Befunge version 93

& read a number 2+ add two .@ display result and exit
  ^- inline comments -^     <-^- other comments

Works with: Befunge version 98

&;read a number;2+;add two;.@;display result and exit;
  ^- inline comments -^     <-^- other comments
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;completely isolated comment block for the paranoid;
;(almost - you can still skip into it.)            ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

Binary Lambda Calculus

BLC has no notion of comments, but since input is considered part of the program, one can always ignore the remainder of input, which can thus be arbitrary. Of course one can have comments in any language that translates to BLC, as discussed in https://rosettacode.org/wiki/Documentation#Binary_Lambda_Calculus

Blast

# A hash symbol at the beginning of a line marks the line as a comment

BQN

# This is a comment

Bracmat

Bracmat uses curly braces as comment delimiters. Curly braces inside comments must be balanced. Comments are so much ignored when source code is read, that they do not reappear in listings created by the built-in lst$ function, an otherwise very useful function to autoindent your code.

Brainf***

This is a comment

Most ASCII characters may be used for comments; only the eight characters "+-<>[],." are Brainf*** commands. Extra care must be used when using punctuation, particularly the comma or period. These are I/O operators and are actually commands rather than comments, and are instead compiled into the program if used and may have to be "debugged" and removed if you forget this issue. Another workaround for this issue is to tactically place the comment inside a "[]" loop which can never be entered (The loop will only be encountered when the active memory cell value is 0).

Brat

# Single line comment

#* Multi
   Line
   Comment *#

Bruijn

Bruijn does not have multi-line comments.

# This is a comment

Brlcad

 # Comments in mget scripts are prefixed with a hash symbol
 ls   # comments may appear at the end of a line

Burlesque

Burlesque does NOT have comments. However, you can comment code by pushing a string and popping it immediately.

"I'm sort of a comment"vv

Since strings are multi-line strings:

"I'm a
very long comment spanning
over several lines"vv

C

/* This is a comment. */
/* So is this
   multiline comment.
 */

The comment starts at the /*, and ends at the */. A comment may be used between any tokens. It cannot be used inside tokens, that is, given the code

struct charisma {};
void f(char/* comment */isma) {}

the function takes an argument of type char, named isma, not an unnamed argument of type charisma.

Comments cannot be nested; that is, if you write

/* some comment /* trying to nest some other comment */ inside */

the comment ends at the first */, and inside */ is again interpreted as source code (almost certainly causing a compile error). Some compilers have the option to allow nested comments, but this is not a standard feature.

Conditional compilation also can be used to make the compiler ignore some text:

#if 0
While technically not a comment, this is also ignored by the compiler
#endif

The trick is that 0 is always false, therefore the text between #if 0 and #endif is never compiled. While this should never be used for actual comments, it's an easy way to comment out some code, especially because it doesn't interfere with normal (documentation) comments.

Conditional compile "comments" can be nested:

#ifdef UNDEFINED
This is not compiled.
#if 0
Nor is this.
#endif
And this still is not compiled.
#endif

Works with: ANSI

Even though the compiler doesn't see #if 0 text, the preprocessor does. Therefore some minimal rules still have to be followed. For example, the following code is not valid:

#if 0	 
This isn't valid.	 
#endif

That's because the preprocessor will interpret the apostrophe as beginning of a character constant, and will complain because that character constant isn't terminated with another apostrophe.

Note that the problem mentioned above cannot occur if there's valid code between the #if 0 and #endif.

Works with: C99

// C++ single-line comments were adopted in the C99 standard.

C#

//This is a comment.
//This is other comment.

/* This is a comment too. */

/* This is a 
multi-line
comment */

C++

See also C

Single line C++-style comments

// This is a comment

C++-style comments start with // and reach up to, but not including, the end of line (more exactly, up to the next unescaped newline). While formally, C++-style comments cannot be nested either, in practice they can:

// This is a valid comment // with a "nested" comment

That's because starting with the first // everything in the line is ignored, including the second //. The fact that the newline is not part of the comment is important for multi-line macro definitions. It means that in the code

#define FOO \
  (macro text) // comment
  (no more macro text)

the line (no more macro text) is not part of the macro definition. Also escaping the line break at the end of the comment with '\' doesn't help, because that would make the third line part of the comment instead. Comments inside macros therefore have to be C-style.

Chapel

// single line

/* multi
line */

Chef

Comment Stew.

This is a comment.
The other comment is a loop, but you can name it anything (single word only).
You can also name ingredients as comments
This is pseudocode.

Ingredients.
Ingredient list

Method.
Methods.
SingleWordCommentOne the Ingredient.
Methods.
SingleWordCommentTwo until SingleWordCommentOned.
Methods.

ChucK

<-- Not common 
// Usual comment

Clean

Clean comments are similar to C++.

Start = /* This is a multi-
           line comment     */ 17 // This is a single-line comment

In contrast to C++ comments can be nested.

Start = /* This is a comment /* Nested comment */ still a comment */ 17

Clojure

Anything from a semicolon to the end of a line is a comment.

;; This is a comment
(defn foo []
  123) ; also a comment

The (comment) macro will prevent a form from being evaluated, returning nil no matter what is contained in the comment. However the forms inside the comment form must be properly parseable (parentheses balanced, etc.) or an exception will be thrown.

(comment (println (foo)) "bar" :baz 123 (System/exit 0))  ;; does nothing, returns nil

Finally, the #_ reader macro will cause a form to be ignored by the reader. Unlike (comment), this does not return nil; the surrounding code is evaluated as though the ignored form isn't even there.

(+ 1 (comment "foo") 3)  ;; Throws an exception, because it tries to add nil to an integer
(+ 1 #_"foo" 3)          ;; Returns 4

CMake

Line comments use the common # syntax:

# A single-line comment

Multi-line comments use a Lua-like square-bracket syntax.

#[[A multi-line
   comment ]]
#[==[A multi-line comment
     with [[nested brackets]]. ]==]

The number of equals signs (=) in the opening bracket determines the number expected in the closing bracket.

COBOL

Fixed format

      * an asterisk in 7th column comments the line out

A D in the 7th column indicates a debugging line which is treated like a comment unless a compiler flag is set.

      D    DISPLAY "Debug"

Free format

*> This comment syntax was defined (with free format code) in COBOL 2002.

Works with: GnuCOBOL

This indicates a debugging line like above, but if it is used in fixed format files, it must be in the 8th column or beyond. Not necessarily. GnuCOBOL also supports D as an indicator in column 7, the >>D format works (more by trickery than spec) if the angle brackets start in column 5, the D ending up in column 7. The >>D debug marker can then be both fixed and free form compatible.

>>D DISPLAY "Debug"

`NOTE` statement

Works with: OS/VS COBOL

This statement causes everything following it up to the next separator period to be treated as a comment. This statement was deleted in COBOL-74.

           NOTE this paragraph is
               commented out and ignored
           .

`REMARKS` and other statements

Works with: GnuCOBOL

There are quite a few IDENTIFICATION DIVISION obsolete and extension reserved words that will work in GnuCOBOL 2.

        IDENTIFICATION DIVISION.
        PROGRAM-ID. program.

        AUTHOR. Rest of line ignored.
        REMARKS. Rest of line ignored.
        REMARKS. More remarks.
        SECURITY. line ignored.
        INSTALLATION. line ignored.
        DATE-WRITTEN. same, human readable dates are allowed for instance
        DATE-COMPILED. same.
        DATE-MODIFIED. this one is handy when auto-stamped by an editor.

Those lines can occur multiple times each within the IDENTIFICATION DIVISION. There can be many AUTHORs, SECURITY notes, etc. These words are also supported by other COBOL dialects, but may have different rules on order, multiples allowed of if full stop periods are required (or allowed) before the end of line.

CoffeeScript

# one line comment

### multi
line
comment ###

ColdFusion

In tags:

As ColdFusion's grammar is based around HTML syntax, commenting is similar to HTML.
<!--- This is a comment.  Nothing in this tag can be seen by the end user.
       Note the three-or-greater dashes to open and close the tag. --->
<!--  This is an HTML comment.  Any HTML between the opening and closing of the tag will be ignored, but any ColdFusion code will still run.
       Note that in the popular FuseBox framework for ColdFusion, the circuit.xml files require that you use this style of comment. -->

In script:

/* This is a comment */
// This is also a comment

Common Lisp

Common Lisp provides line comments (;) and block comments (#|...|#).

Block comments can nest (#|...#|...|#...|#), unlike block comments in e.g. C.

In a common convention, header comments are prefaced with four semicolons, top-level (function level) comments use three, comments for sections of code use two, and margin comments use one.

;;;; This code implements the foo and bar functions

;;; The foo function calls bar on the first argument and multiplies the result by the second.
;;; The arguments are two integers
(defun foo (a b)
   ;; Call bar and multiply
   (* (bar a) ; Calling bar
      b))

;;; The bar function simply adds 3 to the argument
(defun bar (n)
   (+ n 3))

However, comments should not be used for inline documentation, as most defining constructs permit a documentation string (which is then available at runtime).

(defun bar (n)
  "Add 3 to the argument."
  (+ n 3))

(defclass button (widget)
  (label action)
  (:documentation "This is a push-button widget."))

Component Pascal

(* Comments (* can nest *) 
   and they can span multiple lines.
 *)

Crystal

# currently, Crystal only supports single-line comments

# This is a doc comment. Any line *directly* above (no blank lines) a module, class, or method is considered a doc comment
# Doc comments are used to generate documentation with `crystal docs`
class Foo
end

D

void main() {
    // A single line comment.

    /* This is a simple C-style comment that can't be nested.
    Comments mostly work similar to C, newlines are irrelevant.
    */

    /+ This is a nestable comment
      /+ See?
      +/
    +/

    /// Documentation single line comment.

    /**
    Simple C-style documentation comment.
    */

    /++
    Nestable documenttion comment.
    +/
}

Dart

// This is a single line comment, which lasts until the end of the line. The Dart linter prefers this one.

/* This is also a valid single line comment. Unlike the first one, this one terminates after one of these -> */

/*
  You can use the syntax above to make multi line comments as well.
  Like this!
*/

/// These are doc comments. You can use dartdoc to generate doc pages for your classes with these.
/// 
/// Formatting [variable] and [function] names like so allows dartdoc to link to the documentation for those entities.

dc

There is no comment syntax in POSIX dc. The convention is to make a string on the stack and move it to an unused register; a no-op.

[Making and discarding a string acts like a comment] sz

GNU dc added the comment syntax of many other scripting languages.

# remainder of line is a comment

Delphi

See also Pascal

In addition to Pascal, Delphi also allows C++ style single line comments:

// single line comment

Deluge

Comments are only allowed in places such as "on load" scripts. You cannot put them in form or view definitions.

// single line comment

Dragon

// This is a comment

/*
  This is
  a multiple
  line comment.
 */

showln "Hello " /* This is an inline comment */ "world"

DWScript

(* This is a comment.
   It may extend across multiple lines. *)

{ Alternatively curly braces
  can be used. }

/* C-style multi-line comments 
   are supported  */

// and single-line C++ style comments too

Dyalect

/* This is a
multi-line comment */

//This is a single-line comment

Dylan

// This is a comment

/* 
   This is a comment
   that spans multiple
   lines 
*/

Déjà Vu

#this is a comment
!print "this is not a comment, obviously" #this is a comment as well

E

# This is a regular comment.

? "This is an Updoc comment, which
> is an executable example or test case.".split(" ")
# value: ["This", "is", "an", "Updoc", "comment,", "which
#        is", "an", "executable", "example", "or", "test", "case."]

All comments span to the end of the line; there are no paired-delimiter comment syntaxes. “#” begins a comment anywhere outside of quotes; “?” and “>” begin comments only if they are at the beginning of a line (except for whitespace), because those characters are also used for infix operators.

In Updoc, “?” indicates the beginning of a program fragment, “>” the continuation of one, and “#” begins the expected output from its evaluation; “??” indicates special directives.

EasyLang

# This is a comment

EchoLisp

666 ; this is an end-of-line comment

#| 
 This is a multi-line comment
 Nesting is not allowed
|#

;; The (info <name> [<string>)] function associates a symbol and a comment
;; These info strings are saved in permanent memory (local storage)
;; Unicode characters may be used, as everywhere in the language

(define mynumber 666) → mynumber
(info 'mynumber "👀 Symbols may be commented with an information string 👺")
(info 'mynumber) → displays the above inside the 'info' field.

ECL

Single-line comments must begin with //

// this is a one-line comment

Block comments must be delimited with /* and */

 /* this is a block comment - the terminator can be on the same line
or any succeeding line – everything in between is ignored */

Ecstasy

Comments in Ecstasy follow the two forms used by most C-family languages:

/*
 * This is a multi-line comment.
 */
Int i = 0;     // This is an end-of-line comment

ed

# A single-line comment.
# The only type of comment, really.
# No block comments in ed

EDSAC order code

EDSAC programs were handwritten on "programme sheets" designed for the purpose. The programmer, or a computer operator, then copied the "orders" (instructions) to punched tape for input to the machine. Programme sheets had a column for "notes" (comments), but these were not copied to the tape. Modern simulators, however, accept square brackets as comment delimiters.

[This is a comment]
[
And so
is
this
]
[But in 1949 they wouldn't have been]

EGL

See Java

Eiffel

-- inline comment, continues until new line

Ela

//single line comment

/*multiple line
comment*/

Elena

//single line comment

/*multiple line
comment*/

Elixir

Elixir does not have multiple line comments.

# single line comment

Elm

-- a single line comment

{- a multiline comment
   {- can be nested -}
-}

Emacs Lisp

A comment is started by ; and reaches to the end of the line.

; This is a comment

There are some coding conventions for ;; align to indentation, ;;; sections, etc,

http://www.gnu.org/software/emacs/manual/html_node/elisp/Comment-Tips.html

Another way to add comments is to use strings at places where the result of an expression is ignored, since they simply evaluate to themselves without any effect. Note that strings can be multi-line:

"This is effectively a comment,
if used at a place where the result is ignored"

Note that strings at the beginning of function definitions are interpreted as documentation strings for the function (i.e. Emacs will display them if asked for help about the function), e.g.

(defun subtract-second-from-first (x y)
  "This function subtracts its second argument from its first argument."
  (- y x))

Due to this, it's debatable if the string at that place can be considered as comment.

EMal

# This is a line comment.
^|This is a single line block comment.|^

^| This is
 | a multi-line
 | block comment.
 |^

^|This is a ^|nested|^ block comment.|^

Erlang

% Erlang comments begin with "%" and extend to the end of the line.

ERRE

! Standard ERRE comments begin with ! and extend to the end of the line

PRINT("this is code") ! comment after statement

Euphoria

Single line comment:

-- This is a comment

Multiline C-style comment:

/*
This is a comment
*/

Works with: Euphoria version 4.0.0

F#

F# accepts C++ type line comments and OCaml type block comments

// this comments to the end of the line
(* this comments a region
   which can be multi-line *)

Factor

! Comments starts with "! "
#! Or with "#! "
! and last until the end of the line

USE: multiline
/* The multiline vocabulary implements
   C-like multiline comments. */

Falcon

Falcon supports C-language style single line and block comments. A single line comment begins with two slashes (//) and ends at the end of the line. A block comment begins with a slash followed by an asterisk, and terminates when an asterisk followed by a slash is met (/*...*/).

/* Start comment block
 My Life Story
 */

// set up my bank account total
bank_account_total = 1000000 // Wish this was the case

FALSE

{comments are in curly braces}

Fancy

# Comments starts with "#"
# and last until the end of the line

Fennel

; This is a single-line comment

Fermat

Function Foo(n) = 
    {Comments within a function are enclosed within curly brackets.}
    {You can make multi-line comments
        such as this one.}
    n:=n^2 + 3n - 222;   {Comments can go after a semicolon.}
    n:=n+1;
    n.

; comments between functions are preceded by semicolons, like this

Function Bar(n) =
    2n-1.

Fish

Since ><> is a funge-like language, all characters not touched by the command pointer or modified by the p and g commands can be comments. Unlike Brainf***, unknown commands are not ignored by the compiler, they just raise an error.

v This is the Fish version of the Integer sequence task
>0>:n1+v all comments here
  ^o" "< still here
And of course here :)

Forth

Standard Forth includes a number of ways to add comment text. As with everything in Forth, comment characters are actually words that control the compiler.

\ The backslash skips everything else on the line
( The left paren skips everything up to the next right paren on the same line)

Traditionally, the paren comments are used for "stack effect" notation:

: myword ( a b -- c )  ...

This comment means "myword takes two cells on the stack and leaves one". Sometimes, stack effect comment names give clues about the word's function:

: add'em ( a b -- a+b )   + ;
: strlen ( addr -- len )   count nip ;

Some Forth systems implement other commenting words, such as these words from Win32Forth:

\s skips all remaining text in the file
(( skips until the next double-paren, 
   stretching across multiple lines ))
comment:
   Ignore all text in this section
comment;
doc
   Another comment block
enddoc
/* C-style comment */
(* Pascal-style comment *)

Fortran

Compiler: ANSI FORTRAN 77 or compatible (like g77 -strict)

The first six columns in Fortran are traditionally reserved for labels and certain special characters. In particular the letter "C" in the first column indicates a comment:

C     This would be some kind of comment
C     Usually one would avoid columns 2-6 even in a comment.

Some Fortran compilers have the extension that comments starting with D are treated as non-comments if a special debugging flag is given at the compiler invocation. For example:

C     If compiled in debugging mode, print the current value of I
D     PRINT *, I

ISO Fortran 90 or later have an inline comment (!) syntax:

real :: a = 0.0   ! initialize A to be zero

In ISO Fortran 90 or later, "C in first column" comments are only allowed in the "fixed" source form familiar to FORTRAN 77 programmers. The "free" source form only has inline comments (!).

ISO Fortran 95 or later has an optional conditional compilation syntax. If present, it can be used (abused?) to (in effect) comment out blocks of code:

?? if (.false.) then
do while (oh_no)
   a = bad_news()
   b = big_mistake()
   c = gigo()
end do
?? end if

FreeBASIC

' FB 1.05.0 Win64

' This a single line comment

REM This is another way of writing a single line comment

/' 
  This is a
  multi-line
  comment
'/

/' 
  Multi-line comments
  /'
    can also be nested
  '/
  like this
'/

Frink

// This is a single-line comment
/*  This is a comment
    that spans multiple lines
    and so on.
*/

Futhark

-- Single-line comment

-- Multi-line
-- comment (yes, just several single-line comments).

FutureBasic

//  Single line comment
rem Single line comment
/*  Single line comment  */

/*
  Multiline
  comment
*/

FUZE BASIC

//Comment (No space required)
# Comment (Space required)
REM Comment (Space require)
PRINT "This is an inline comment."//Comment (No space required)
END

Gambas

In gambas, comments can be inserted by prefixing them with an apostrophe. The gambas interpreter will ignore the apostrophe and any other characters that follow it until the end of the line:

 ' This whole line is a comment and is ignored by the gambas interpreter
 print "Hello" ' Comments after an apostrophe are ignored
 '' A bold-style comment
 ' TODO:  To Do  comment will appear in Task Bar
 ' FIXME: Fix Me comment will appear in Task Bar
 ' NOTE:  Note   commnet will appear in Task Bar

GAP

# Comment (till end of line)

gecho

( this is a test comment... o.O ) 1 2 + .

Gema

! comment starts with "!" and continues to end of line

A shebang (#!) may be used as a comment in the first line of a file.

Genie

Genie allows comments in code in two different ways.

// Comment continues until end of line

/* Comment lasts between delimiters */

Delimited comments cannot be nested.

GML

single-line comment:

 // comment starts with "//" and continues to the end of the line

multi-line comment:

 /* a multi-line comment starts with slash-asterisk and,
ends with asterisk-slash.
also note:
 * A multi-line comment is ignored inside a string
 * A multi-line comment can be ended inside a line
*/

gnuplot

# this is a comment

# backslash continues \
a comment to the next \
line or lines

The way backslash continues a comment means that comments can't usefully be put within a multi-line function definition,

# this doesn't work
foo(n) = (n                \
          + 2    # no good \
          + 3)          

# behaves as if you wrote merely
foo(n) = (n+2

Go

// this is a single line comment
/* this is
   a multi-line
   block comment.
/* It does not nest */

Golfscript

# end of line comment

Gri

# through to newline.

# this is a comment
show 123        # this too is a comment

// works similarly but is reckoned the "old way" (as of Gri 2.12.23)

// this is a comment
show 123        // this too is a comment

Both forms can be used in input data files too.

Groovy

See Java

GW-BASIC

Works with: GW-BASIC

100 REM Standard BASIC comments begin with "REM" (remark) and extend to the end of the line
110 PRINT "this is code": REM comment after statement

Haskell

i code = True -- I am a comment.

{- I am also
   a comment. {-comments can be nested-}
   let u x = x x (this code not compiled)
   Are you? -}

-- |This is a Haddock documentation comment for the following code
i code = True
-- ^This is a Haddock documentation comment for the preceding code

{-|
  This is a Haddock documentation block comment
-}
i code = True

Haxe

// Single line commment.

/* 
   Multiple
   line
   comment.
*/

HicEst

! a comment starts with a "!" and ends at the end of the line

Hope

! All Hope comments begin with "!" and extend to the end of the line

HTML

<!-- Anything within these bracket tags is commented, single or multi-line. -->

Icon and Unicon

Any text after "#" is a comment.

# This is a comment

procedure x(y,z)    #: This is a comment and an IPL meta-comment for a procedure

The The Icon Programming Library established conventions for commenting library additions and functions. This included both header block comments and meta comments on procedures within library files.

IDL

The comment character in IDL is the semicolon - everything starting with it and to the end of the line is a comment. Like this:

; The following computes the factorial of a number "n"
fact = product(indgen( n )+1) ; where n should be an integer

Inform 7

[This is a single-line comment.]

[This is a
multi-line comment.]

[Comments can [be nested].]

Insitux

;this is a comment; and using semicolons here is fine

(+ 2 2) ;this is a comment

"this string will be ignored if in the top scope
which can also stretch across
multiple lines"

(do "if you're desperate, using do will make sure this string will not be returned also"
  (+ 2 2))

Intercal

PLEASE NOTE This is a comment

Io

# Single-line comment

// Single-line comment

/* Multi-line
   comment */

Isabelle

theory Text
imports Main
begin

(* Top-level Isar comment. *)

end

J

NB. Text that follows 'NB.' has no effect on execution.

'Character strings in J may have their value be ignored and treated as comment text.'

0 : 0
Multi-line comments may be placed in strings,
like this.
)

Note 'example'
Another way to record multi-line comments as text is to use 'Note', which is actually
a simple program that makes it clearer when defined text is used only to provide comment.
)

{{)n
  J release 9's nestable blocks can be used as comments.

  Typically, this would be in contexts where the blocks would not be used.
  That said, "literate coding practices" may stretch the boundaries here.

  Also, noun blocks (beginning with ')n') avoid syntactic concerns about content.

  These blocks even allow contained '}}' sequences to be ignored (unless, of
  course the }} character pair appears at the beginning of a line).
}}

Java

Java has two ways to enter normal comments, plus a third type of comment that doubles as a way to generate HTML documentation.

C Style

/* This is a comment */

/*
 * This is
 * a multiple
 * line comment.
 */

This C-style comment starts with /* and ends with */. The two delimiters may be on the same or separate lines. This style comment may be used anywhere white space is permitted.

C++ Style (inline)

// This is a comment

This C++-style comment starts with // and extends to the end of line.

Java Documentation (Javadoc)

/** This is a Javadoc comment */

/**
 * This is
 * a multiple
 * line Javadoc comment
 */

Javadoc is a standardized documentation code for Java. Its comments begin with a forward slash and two stars. Javadoc comments have different tags that signify different things in the methods and classes that they precede.

Sneaky

Your editor will probably colour this as great big comment, but it compiles and prints "Hello World!". Once you've figured out how this works, try this discussion on why it's allowed.

public class JustComments {
    /*
    \u002A\u002F\u0070\u0075\u0062\u006C\u0069\u0063\u0020\u0073\u0074\u0061\u0074\u0069\u0063
    \u0020\u0076\u006F\u0069\u0064\u0020\u006D\u0061\u0069\u006E\u0028
    \u0053\u0074\u0072\u0069\u006E\u0067\u005B\u005D\u0061\u0072\u0067\u0073\u0029
    \u007B\u0053\u0079\u0073\u0074\u0065\u006D\u002E\u006F\u0075\u0074\u002E
    \u0070\u0072\u0069\u006E\u0074\u006C\u006E\u0028\u0022\u0048\u0065\u006C\u006C\u006F\u0022
    \u002B\u0022\u0020\u0057\u006F\u0072\u006C\u0064\u0021\u0022\u0029\u003B\u007D\u002F\u002A
    */
}

JavaScript

n = n + 1; // This is a comment

// This is a valid comment // with a "nested" comment

/* This is
a multi line
comment
// with a "nested" comment
and another line in the comment
*/

JCL

first form

//* This is a comment line (//* in columns 1-3)

second form

/* This is also a comment line (/*  in columns 1-3)

Joy

# this is a single line comment

(* this is a
multi-line comment *)

Multi-line comments cannot be nested.

jq

Except when a hash symbol (#) appears within a string, it begins a comment that continues to the end of the line:

# this is a single line comment
"Hello #world" # the first # on this line is part of the jq program

Jsish

#!/usr/bin/env/jsish
/* Comments, in Jsish */

// to end of line comment, double slash

/*
 Enclosed comment, slash star, ending with star slash
 Cannot be nested, but can cross line boundaries and occur
 pretty much anywhere whitespace is allowed
*/

var x = 'X'; /* A var called X */
/* active code on this line */ printf("Result %q %d\n", /* comment code mix */ x, /**/42);

;x;
// jsish also handles double slash commented
// unit test echo lines as a special case of "expect failure"

;//noname(x);

/*
=!EXPECTSTART!=
Result X 42
x ==> X
noname(x) ==>
PASS!: err = can not execute expression: 'noname' not a function
=!EXPECTEND!=
*/

Output:

prompt$ jsish comments.jsi
Result X 42
prompt$ jsish --U comments.jsi
Result X 42
x ==> X
noname(x) ==>
PASS!: err = can not execute expression: 'noname' not a function
prompt$ jsish -u comments.jsi
[PASS] comments.jsi

Julia

# single line

#=
Multi-
line
comment
=#

K

  / this is a comment
  2+2  / as is this

KonsolScript

//This is a comment.
//This is another comment.

/* This is a comment too. */

/* This is a 
multi-line
comment */

Kotlin

// This is a single line comment

/*
    This is a 
    multi-line
    comment
*/

/*
    Multi-line comments
    /*
        can also be nested
    */
    like so
*/

const val CURRENT_VERSION = "1.0.5-2"  // A comment can also be added at the end of a line
const val /* or even in the middle of a line */ NEXT_MAJOR_VERSION = "1.1"

/**
 * This is a documentation comment used by KDoc.
 *
 * It's documenting the main function which is the entry-point to a Kotlin executable.
 *
 * @param [args] A string array containing the command line arguments (if any) passed to the executable
 * @return Implicit return value is Unit which signifies no meaningful return value (like 'void' in java)
 */
fun main(args: Array<String>) {
    println("Current stable version is $CURRENT_VERSION")
    println("Next major version is $NEXT_MAJOR_VERSION")
}

Lambdatalk

Out of bracketed expressions words are ignored by the lambdatalk evaluator and are dislayed as they are:

Hello World
-> Hello World

In order to prevent any evaluation and display of some parts of code put them inside triple degrees "°°°": 

°°°
this is
   a comment ... and an expression {+ 1 2}
     on several lines
°°°

LabVIEW

This image is a VI Snippet, an executable image of LabVIEW code. The LabVIEW version is shown on the top-right hand corner. You can download it, then drag-and-drop it onto the LabVIEW block diagram from a file browser, and it will appear as runnable, editable code.

Lang

Single line

# This is a comment

Multiline (Line continuation)

# This is a comment\
with multiple lines

Multiline (Multiline text sequence)

# {{{This is a comment
which has more than
2 lines
and this one}}}

Lang5

# This is a comment.

langur

Langur has 2 types of comments.

# single line comment starts with hash mark

/* inline or multi-line comment uses C-style syntax */

Lasso

//This is a comment.

/* This is also a comment. */

/* A multi-line
comment */

/* ==========================
A multi-line
comment 
=========================== */

$L a T e X$

In LaTeX, comments look like this:

\documentclass{minimal}
\begin{document}
% This is a comment
\end{document}

LaTeX comments start with % and continue up to and including the line break. The fact that the line break itself is commented out as well makes it useful for adding line breaks in the source code of complex macros without LaTeX interpreting them (which may cause extra space or even a paragraph break in the resulting typeset text). For example, the following results in the one word "understandable":

\documentclass{minimal}
\newcommand{\firstpart}[1]{under#1}
\newcommand{\secondpart}{able}
\newcommand{\complete}{%
\firstpart{stand}%
\secondpart}
\begin{document}
\complete
\end{document}

Without the percent sign after \firstpart{stand}, it would have been the two words "understand able".

Liberty BASIC

'This is a comment
REM This is a comment

print "This has a comment on the end of the line." 'This is a comment
print "This also has a comment on the end of the line." : REM This is a comment

Lily

There are two kinds of comments:

# This is a single-line comment

and

#[ This
is
a
block
comment ]#

Like with C, block comments don't nest.

LilyPond

% This is a comment

%{ This is a comment
spanning several lines %}

Lingo

In Lingo any line starting with "--" is a comment and ignored by the interpreter.

-- This is a comment.
-- This is another comment

LiveCode

-- comment may appear anywhere on line
// comment may appear anywhere on line
# comment may appear anywhere on line
/*  this is a 
block comment that
may span any number of lines */

Logo

; comments come after a semicolon, and last until the end of the line

Logtalk

% single-line comment; extends to the end of the line

/* multi-line
comment */

LOLCODE

OBTW This is a
multi line comment
TLDR

BTW This is a single line comment.

LotusScript

LotusScript has two ways to enter comments.

' This is a comment

Wherever the single quote (') is used, the rest of the line is treated as a comment and ignored. Multi-line comments would each need a single quote mark. This style of comment is usually used for making small in-line or single line comments.

%REM
This is a multi- 
line comment.
%END REM

A %REM marker begins a comment block, and a %END REM marker ends the comment block. This style of comment is used for making longer multi-line comments, often at the beginning of a class, sub or function.

LSE

* Ceci est un commentaire qui prend fin quand la ligne se termine

(* Ceci est un commentaire sur plusieurs lignes
comme vous pouvez le voir puisqu'il s'étend sur
plusieurs lignes justement... *)

(* Cette exemple est selon la revision LSE-2000 *)

LSE64

# single line comment (space after # is required)

The author of LSE64 comments the stack effect of words with header comments as follows:

# arg1 arg2 '''yields''' result|''nothing''

Lua

-- A single line comment

--[[A multi-line 
    comment --]]

Works with: Lua version 5.1 and above

--[====[ A multi-line comment that can contain [[ many square brackets ]]
]====]

M2000 Interpreter

Multiline commend Ret { lines of code, or text }

Same line comment until end of line (can start immediate after a command: use ' or \ or //

Rem (form start of code line)

(:\ and \\ or \) in a name can exist only for Dir statement:

dir c:\thatfolder

is the same as

dir "c:\thatfolder"

Module Comments {
	Rem {
		Print "no print here"
		? "no print here either"
	}
	Rem : single line remark
	// single line
	\ single line
	' single line
	? "ok" : Rem : Print "not print - but code have syntax highlight" 
	? "ok" // single line - start without double colon
	? "ok" \ single line - start without double colon
	Print "ok" ' single line
}
Comments

M4

eval(2*3)  # eval(2*3)  "#" and text after it aren't processed but passed along

dnl  this text completely disappears, including the new line

divert(-1)
Everything diverted to -1 is processed but the output is discarded.
A comment could take this form as long as no macro names are used.
divert

Output:

6  # eval(2*3)  "#" and text after it aren't processed but passed along

dnl must be a separate word. An empty pair of quotes can separate it from preceding text if necessary

some text`'dnl then a deleted comment

changecom() can set a different character for #,

changecom(%)
% now percent prevents macro expansion

In GNU m4 an empty changecom() string means no such commenting char at all (but in BSD m4 means reset to the default #)

changecom()
GNU m4 now no macro expansion suppression character at all

In GNU m4 changecom() also takes separate start and end strings and they can be multi-character sequences, allowing for example C style,

changecom(/*,*/)
/* GNU m4 now no macro expansion in C style comments */

Maple

x := 4: x; # Everything on this line, after this, is a comment.

17; (* This
   is
   a multiline comment *) 23.4;

Output:

                               4
                               17
                              23.4

Mathematica / Wolfram Language

(*this is a comment*)

It can be used everywhere and nested if necessary:

If[a(*number 1*)<(* is smaller than number 2*) b, True (*return value (*bool true*)*), False (*return bool false*)]

evaluates to:

If[a < b, True, False]

MATLAB

%This is a comment
%% Two percent signs and a space are called a cell divider

Maxima

/* Comment
  /* Nested comment */
*/

MAXScript

-- Two dashes precede a single line comment

/* This is a
   multi-line comment */

MBS

! A pling in a line starts a comment

INT   n:=5   ! Comments can appear at the end of a line

/* A comment block can also be defined using climbstar and starclimb symbols. 
  This allows comments to be stretched across several lines */

MEL

// This is a single line comment

Metafont

% this is "to-end-of-line" comment

Microsoft Small Basic

Microsoft Small Basic uses the quote symbol to mark it's comments. After placing a quote everything in that line will be ignored.

' This is a comment
i = i + 1  ' You can also append comments to statements

min

Works with: min version 0.19.3

; this is a comment
1 1 + ; add one and one together

MiniScript

MiniScript just has one kind of comment. They begin with two slashes, and extend to the end of a line. So you can put a comment either on a line by itself, or after a statement.

// How many roads must a man walk down?
x =  6 * 7  // forty-two

Mirah

puts 'code' # I am a comment
/* This is
 * a multiple
 * line comment */

MIPS Assembly

This is ultimately up to the assembler, but semicolons are typically the comment character for almost all assemblers.

;this is a comment
li $t0,0x1234     ;this is also a comment

However, MARS and QTSPIM use the #.

# this is a comment
li $t0,0x1234     # this is also a comment

mIRC Scripting Language

;Single Line Comment
/*
Multiple
Line
Comment
*/

Modula-2

(* Comments (* can nest *) 
   and they can span multiple lines.
 *)

Modula-3

(* Comments (* can nest *) 
   and they can span multiple lines.
 *)

Monte

# This comment goes to the end of the line
/** This comment is multi-line.
    Yes, it starts with a two stars
    and ends with only one.
    These should only be used for docstrings. */

MontiLang

/# This is a comment #/
/# 
comments can span multiple lines 
nested comments are not supported #/

MOO

"String literals are technically the only long-term comment format";
// Some compilers will, however, compile // one-liners to string literals as well (and vice-versa)
/* Classical C-style comments are removed entirely during compile */

Nanoquery

Comments in Nanoquery must be on a single line.

// this is a comment
// this is also a comment

NATURAL

* This is a comment and extends to the end of the line

Neko

// Single line comment, of course!

/*
Multi line comment!
*/

/**
Documentation block
<doc>can include XML parsed nodes between doc tags</doc>
**/

Nemerle

// This comment goes up to the end of the line
/* This
is
a
multiline
comment */

NESL

% This is a comment. %

NetRexx

NetRexx supports block-comments and line comments. Block comments are started with a /* and terminated with a */. Line comments follow a -- sequence anywhere on a line. NetRexx supports nested comments (see REXX).

/*

 NetRexx comment block

*/

-- NetRexx line comment

NewLISP

A comment is started by ; and reaches to the end of the line.

; This is a comment

Nim

# Nim supports single-line comments

var x = 0 ## Documentation comments start with double hash characters.

var y = 0 ## Documentation comments are a proper part of the syntax (they're not discarded by parser, and a real part of AST).

#[
There are also multi-line comments
Everything inside of #[]# is commented.
]#

# You can also discard multiline statements:

discard """This can be considered as a "comment" too
This is multi-line"""

Nix

# This comment goes up to the end of the line
/* This
is
a
multiline
comment */

NSIS

# This is a comment that goes from the # to the end of the line.
; This is a comment that goes from the ; to the end of the 
 
/* This is a 
multi-line
comment */

Oberon-2

(* this is a comment *)
(* 
   and this is a
   multiline comment
   (* with a nested comment *)
*)

Objeck

#This is a comment.
# This is other comment.
 
#~ This is a comment too. ~#
 
#~ This is a 
multi-line
comment ~#

Objective-C

See C

OCaml

(* This a comment
   (* containing nested comment *)
 *)

(** This an OCamldoc documentation comment *)

Octave

# I am a comment till the end of line
% I am a comment till the end of line

%{
  This comment spans
  multiple lines
%}

Oforth

Oforth has only single line comment (inside or outside definition)

// This is a comment...

ooRexx

Comments in ooRexx follow the same rules as REXX and NetRexx

/*
  Multi-line comment block
 */

-- this type of comment works in ooRexx, NetRexx and some of the more popular REXX implementations like Regina

hour = 0  -- which is, like midnight, dude.

hour = 12 /* time for lunch! works as well (and really everywhere) */

Openscad

The openscad geometry compiler supports C++ style comments:

// This is a single line comment

/*
  This comment spans
  multiple lines
*/

OxygenBasic

'  Basic line comment
;  Assembly code line comment
// C line comment
/* C block comment */

Oz

% one line comment

%% often with double "%" because then the indentation is correct in Emacs

/* multi line
   comment
*/

PARI/GP

Comments are similar to C. The block comment is identical: /* comment */. The line comment uses backslashes instead of slashes: \\ comment.

Pascal

(* This is a comment.
   It may extend across multiple lines. *)

{ Alternatively curly braces
  can be used. }

(* This is a valid comment in Standard Pascal,
   but not valid in [[Turbo Pascal]]. }

{ The same is true in this case *)

In Pascal, comments cannot be nested.

PascalABC.NET

(* This is a 
   multiline comment *)

{ This is also a 
   multiline comment }

//  This is a single line comment

PASM

# This is a comment
print "Hello\n"    # This is also a comment
end

Peloton

Peloton encloses all comments inside <@ OMT></@> (fixed length opcode) or <# OMIT></#> (variable length opcode) whether single- or multi- line.

<@ OMT>This is a
multiline
comment</@>

OMT suppresses evaluation of everything contained. There are a variety of extra opcodes which can be used to control how OMT functions at run time.

Perl

Works with: Perl version 5.x

Single line comment

# this is commented

These may also be at the end of a line

my $var = 1; # this is the comment part

Multi-line comments for inline documentation (Plain Old Documentation, or POD in Perl parlance) follow the format:

=pod

Here are my comments
this is multi-line

=cut

Note that technically, both of the lines beginning with the equals sign must be surrounded on either side for compatibility with all "POD" parsers.

Note also that any string beginning with an equals sign, and that appears in the initial column of a line, begins a multi-line comment. It does not have to be a POD "command:" the following are all valid:

=head1
=head4
=over 4
=Any Old String

Such blocks always end in =cut.

For more info, type at a command prompt (or into a search engine): "perldoc perlpod"

Phix

Library: Phix/basics

Single line comment:

-- this is a comment.
// this is also a comment.

Nestable multiline comments:

/*
This is a comment
procedure oldproc()
   /*
     This is also a comment
   */
   puts(1,"kill me now")
end procedure
*/
puts(1,"this is not a comment")

Output:

this is not a comment

In fact there are now a total of six(!) different types of comment in Phix:

#! opening shebang
#[ .. #] for multiline shebangs
-- standard line comments
// C-style line comments
/* .. */ standard nestable multiline comments
--/* .. --*/ Euphoria-compatibility-style nestable multiline comments/code

PHP

Single line comment:

# this is commented
// this is commented

These may also be at the end of a line:

$var = 1; # this is the comment part
$var = 1; // this is the comment part

Basic syntax for multi-line comments:

/*
Here are my comments
this is multi-line
*/

Note that; it is more common to see phpDocumentor styled multi-lined comments:

/**
 * phpdoc Comments
 * @todo this is a todo stub
 */

Picat

Works with: Picat

/*
 * Multi-line comment
 */

% Single-line Prolog-style comment

PicoLisp

# The rest of the line is ignored
#{
   This is a
   multiline comment
}#
NIL
Immediately stop reading this file. Because all text in the input file following
a top-level 'NIL' is ignored.

This is typically used conditionally, with a read-macro expression like
`*Dbg
so that this text is only read if in debugging mode.

Pike

// This is a comment.
/* This is a 
   multi
   line
   comment */

int e = 3; // end-of-statement comment.

PL/I

/* This is a comment. */

/* 
This is a multiline comment. 
*/

Note: In PL/I, comments cannot be nested.

PL/SQL

Single line comment:

--this is a single line comment

Multiline comment:

/*
this is a multiline
comment
*/

End of line comment:

v_var number; --this is an end of line comment

Plain English

\A comment like this lasts until the end of the line
Put 1 plus [there are inline comments too] 1 into a number.

Plain $T e X$

The default raw/bare TeX assigns the category code 14 (comment character) to the character %, and plainTeX, as also LaTeX (see here Comments in LaTeX, does not change it; so the % starts a to-end-of-line comment in many TeX macro packages.

% this is a comment
This is not.

The final newline character is eaten and since it normally behaves like a space, the comment can be used to hide the newline:

\def\firstpart#1{under#1}
\def\secondpart{able}
\def\complete{\firstpart{stand}%
\secondpart}

\complete

Outputs understandable; without % it would output understand able.

Pop11

Pop11 has two kinds of comments: endline and C-like. Endline comment begins with tree consecutive semicolons and ends at the end of line:

;;; This is a comment

C-like comments may be multiline:

/* First line
   Second line */

C-like comments (unlike C) may be nested:

/* This is a comment /* containing nested comment */ */

One can also use conditional compilation to comment out sections of code

#_IF false
some code 
#_ENDIF

however, commented out part must consist of valid Pop11 tokens. In particular, C-like comments must balance and strings must be terminated. The following is an error:

#_IF false
This w'ont work
#_ENDIF

because apostrophe starts an unterminated string.

PostScript

%This is a legal comment in PostScript

PowerShell

# single-line comment

Works with: PowerShell version 2

<# multi-line
   comment #>

Processing

// a single-line comment

/* a multi-line
   comment
*/

/*
 * a multi-line comment
 * with some decorative stars
 */

// comment out a code line
// println("foo");
 
// comment at the end of a line
println("foo bar"); // "baz"

Processing Python mode

# a single-line comment
 
"""
Not strictly a comment, bare multi-line strings are used
in Python as multi-line comments. They are also used as
documentation strings or 'docstrings' when placed as the
first element inside function or class definitions.
"""
 
# comment out a code line
# println("foo")

# comment at the end of a line
println("foo bar") # "baz"

# there is no way to make an inline comment

ProDOS

I don't know why this is even a task because it should be included in any decent programming language.

IGNORELINE your text here

ProgressBASIC

10 REM I AM A COMMENT

Prolog

% this is a single-line comment that extends to the end of the line

/* This is a
multi-line comment */

PureBasic

PureBasic uses the ";" symbol to mark its comments. All text entered after ";" on a line is ignored by the compiler.

;comments come after an unquoted semicolon and last until the end of the line
foo = 5 ;This is a comment
c$ = ";This is not a comment"  ;This is also a comment

Python

Python uses the "#" symbol to mark it's comments. After placing a "#", everything to the right of it in that line will be ignored.

# This is a comment
foo = 5 # You can also append comments to statements

Certain 'do nothing' expressions resemble comments

"""Un-assigned strings in triple-quotes might be used 
   as multi-line comments
"""

'''
   "triple quoted strings" can be delimited by either 'single' or "double" quote marks; and they can contain mixtures
   of other quote marks without any need to \escape\ them using any special characters.  They also may span multiple
   lines without special escape characters.
'''

Note that strings inserted among program statements in Python are treated as expressions (which, in void context, do nothing). Thus it's possible to "comment out" a section of code by simply wrapping the lines in "triple quotes" (three consecutive instances of quotation marks, or of apostrophes, and terminated with a matching set of the same). Using unassigned strings as comments is frowned on and may also trigger certain linters.

Documentation Strings

Python makes pervasive use of strings which immediately follow class and function definition statements, and those which appear as the first non-blank, non-comment line in any module or program file. These are called "documentation" strings or "docstrings" for short; and they are automatically associated with the __doc__ attribute of the class, function, or module objects in which they are defined. Thus a fragment of code such as:

#!/usr/bin/env python
# Example of using doc strings
"""My Doc-string example"""
 
class Foo:
     '''Some documentation for the Foo class'''
     def __init__(self):
        "Foo's initialization method's documentation"
 
def bar():
    """documentation for the bar function"""
 
if __name__ == "__main__":
    print (__doc__)
    print (Foo.__doc__)
    print (Foo.__init__.__doc__)
    print (bar.__doc__)

... would print each of the various documentation strings in this example. (In this particular example it would print two copies of the first doc string which because __doc__ in the "current" name space is the same as __main__.__doc__ when our program is running as a script). If some other script were to import this file (under the name "example" perhaps) then "My Doc-string example" would be the value of example.__doc__

Python "docstrings" are used by a number of tools to automatically generate documentation (for most of the Python standard libraries, classes, functions, etc, as well as for user programs which define docstrings). They are also used by tools such as doctest to automatically derive test suites from properly formatted examples of class instantiations, function invocations and other usage samples. The standard pydoc utility can search through Python source trees generating documentation and can function as a local web server allowing a programmer to browse "live" hyperlinked documentation of their project.

(As noted above extraneous strings interspersed throughout a Python source file can be used as comments, though this is rarely done in practice; only those strings which lexically follow the definition of a class, function, module or package are assigned to __doc__ attributes in their respective name spaces).

Quackery

 ( The word "(" is a compiler directive (a builder,
   in Quackery jargon) that causes the compiler to 
   disregard everything until it encounters a ")"
   preceded by whitespace. 
 
   If you require more than that, it is trivial to
   define new comment builders...                  )
 
  [ behead carriage = until ] builds #
 
  # Now the word "#" will cause the compiler to
  # disregard everything from the "#" to the end of 
  # the line that it occurs on.
 
  [ drop $ "" ] builds commentary
 
  commentary
   
  The word "commentary" will cause the compiler to
  disregard everything that comes after it to the 
  end of the source string or file.

QB64

CBTJD: 2020/03/12

REM This is a remark...
' This is also a remark...

IF a = 0 THEN REM (REM follows syntax rules)
IF a = 0 THEN '(apostrophe doesn't follow syntax rules, so use END IF after this)
END IF

'Metacommands such as $DYNAMIC and $INCLUDE use the REM (or apostrophe).
REM $STATIC 'arrays cannot be resized once dimensioned.
REM $DYNAMIC 'enables resizing of array dimensions with REDIM.
REM $INCLUDE: 'loads a reference file or library.

R

# end of line comment

Racket

; this is a to-end-of-line coment

#| balanced comment, #| can be nested |# |#

#;(this expression is ignored)

#; ; the following expression is commented because of the #; in the beginning
(ignored)

Raku

(formerly Perl 6)

Single-line comments

A single-line comment starts with # and extends to the end of the line.

# the answer to everything
my $x = 42;

Multi-line comments

A multi-line comment starts with #` and followed by the commented text enclosed by bracketing characters (e.g., (), [], {}, 「」, etc.).

#`( 
    Comments beginning with a backtick and one or more opening bracketing characters are embedded comments.
    They can span more than one line…
)

my $y = #`{ …or only part of a line. } 3;

Multi-line comments can also be embedded into code.

for #`(each element in) my @array {
    say #`(or print element) $_ #`(with a newline);
}

Using more than one bracketing character lets you include an unmatched close bracket, as shown below.

#`{{
  This close curly brace } won't terminate the comment early.
}}

Pod comments

=begin comment

Pod is the successor to Perl 5's POD. This is the simplest way to use it for multi-line comments.
For more about Pod, see Pod: https://docs.perl6.org/language/pod

=end comment

Pod also provides declarator blocks which are special comments that attach to some source code and can be extracted as documentation. They are either #| or #= and must be immediately followed by either a space or an opening curly brace. In short, blocks starting with #| are attached to the code after them, and blocks starting with #= are attached to the code before them.

#| Compute the distance between two points in the plane.
sub distance(
    Rat \x1, #= First point's abscissa,
    Rat \y1, #= First point's ordinate, 
    Rat \x2, #= Second point's abscissa, 
    Rat \y2, #= Second point's ordinate, 
){
    return sqrt((x2 - x1)**2 + (y2 - y1)**2)
}

Rapira

Comments in Rapira are preceded by a backslash (\).

\ This is a Rapira comment.

Raven

 # this is a comment

REBOL

; This is a line comment.

{ Multi-line strings can
  be used as comments 
  if you like }

Functions have special commenting options which make them self documenting:

plus2: func [
    "Adds two to a number."
    n [number!] "The number to increase."
][
    n + 2
]

If you say "help plus2" at REBOL's REPL, you'll get this help information:

   USAGE:
       PLUS2 n
   
   DESCRIPTION:
        Adds two to a number.
        PLUS2 is a function value.
   
   ARGUMENTS:
        n -- The number to increase. (Type: number)

Relation

// This is a valid comment 
// A space is needed after the double slash

Retro

( comments are placed between parentheses. A space must follow the opening parenthesis. )

REXX

It should be noted that comments in the REXX language support nested comments, so comments aren't totally ignored by the REXX interpreter (and compiler).

REXX comments are scanned and preserved for use by the sourceline BIF. [The sourceline BIF allows the retrieval of any or all lines of source (of the REXX program).]

Also, redundant blanks are removed and processed/shown for various trace options (trace is a REXX statement that may show various interpretation/execution stages of REXX statements (clauses, values, etc.), including comments and also blank lines). The trace statement is also used for interactive debugging.

Nested comments must have matching delimiters, so the contents of the comments can't just be willy-nilly characters.

Also, some REXX interpreters show the comment (if part of a REXX statement) as part of the information displayed when (if) a syntax error occurs and an informative error message is generated. For instance, in the program (named c:\COMMENTD.REX):

/*REXX program that demonstrates what happens when dividing by zero.  */
y=7
say 44 / (7-y)      /* divide by some strange thingy.*/

output when using the Regina REXX interpreter:'

     3 +++ say 44 / (7-y)      /* divide by some strange thingy.*/
Error 42 running "c:\COMMENTD.REX", line 3: Arithmetic overflow/underflow
Error 42.3: Arithmetic overflow; divisor must not be zero

output when using the R4 REXX interpreter:'

Error 42 : Arithmetic overflow/underflow (SYNTAX)
Information: Divide by zero
Error occurred in statement# 3
Statement source: say 44/(7-y)
Statement context: c:\commentdv.rex, procedure: commentdv

output when using the Personal REXX interpreter:'

     3 +++ say 44 / (7-y)      /* divide by some strange thingy.*/
Error 42 on line 3 of C:\COMMENTD.REX: Arithmetic overflow/underflow

The REXX language was heavily modeled after PL/I, both languages have the same comment construct, but PL/I doesn't support nested comments.

Nested comments allow an easy way to comment large chunks of code where the commented-out code has its own comments.

/*REXX program to demonstrate various uses and types of comments. */

/* everything between a "climbstar" and a "starclimb" (exclusive of literals) is
   a comment. 
                         climbstar =  /*   [slash-asterisk]      
                         starclimb =  */   [asterisk-slash]

            /* this is a nested comment, by gum! */
            /*so is this*/

Also, REXX comments can span multiple records.

There can be no intervening character between the slash and asterisk  (or
the asterisk and slash).  These two joined characters cannot be separated
via a continued line, as in the manner of:

       say 'If I were two─faced,' ,
           'would I be wearing this one?' ,
           '      --- Abraham Lincoln'

 Here comes the thingy that ends this REXX comment. ───┐
                                                       │
                                                       │
                                                       ↓

                                                       */

    hour = 12       /*high noon                   */
midnight = 00       /*first hour of the day       */
   suits = 1234     /*card suits:   ♥  ♦  ♣  ♠    */ 

hutchHdr = '/*'  
hutchEnd = "*/"

    /* the previous two "hutch" assignments aren't 
       the start  nor  the end of a REXX comment. */

  x=1000000 **   /*¡big power!*/   1000

/*not a real good place for a comment (above), 
  but essentially, a REXX comment can be 
  anywhere whitespace is allowed.            */

A Classic REXX implementation (e.g. Regina) also allow line comments which start with a -- sequence and extend to the end of the line:

[Note: Regina REXX releases since 3.4 allow this type of single-line comment only if the option Single_Line_comments isn't present in the REGINA_OPTIONS environmental variable. So, Regina may allow the use of single-line comments, depending upon which release is being used. That is to say, one can't depend (or assume) that the Regina extension (of single-line comments) for the aforementioned option will be or not be present (supported and/or allowed) in the environment being used]. Which means one could set this option to their preference if using Regina REXX later than version 3.3.

Since Single-Line comments aren't part of the ANSI standard nor a part of the Classic REXX language, the use of which would make the REXX code non-portable.]

-- A REXX line comment (maybe)
say "something" -- another line comment (maybe)

It should be noted that the above type of comments are not part of Classic REXX, nor are they described nor sanctioned in the REXX ANSI standard.

Ring

in Ring language we can use // or # for one line comments:

//this is a single line comment
#this also a single line comment!

and for multi-line comments we use /* */:

/*This is a multi-line
comment that will be completely
ignored by the compiler/interpreter
*/

RLaB

RLaB only has single line comment indicator, as in following examples

x = "code" # I am a comment
x = "code" // Here I comment thee
#  matlab-like document line
// C++ like document line

Robotic

Comments can only be created in one way:

. "This is a comment line"

. "Print Hello world"
* "Hello world."

. "This is the only way to comment a line in Robotic"

Although these are comments, the interpreter doesn't completely ignore it. For one, the code speed can be affected if they are ever encountered. Also, if an @ character exists at the beginning of the comment line, then the rest of the string after it is now the Robot's new name (there is a 14 character limit).

Example of changing the robot's name:

. "@NewRobotName"

This would then change the robot's name from whatever it was before to "NewRobotName" instead.

Rockstar

Rockstar is cool.
(Rockstars don't like comments, but if you really really want to, you write them in parentheses and they are believed to be multiline. In fact, parentheses are just the comment symbols, so you can't even use parentheses in math, so if you want the addition to happen before the multiplication, do the addition and assign it to a variable. And by the way, the Rockstar is cool line assigned the number 4 to the variable Rockstar, because cool is four letters and all that. And this comment has gone on way too long for a language with a developer community that hates comments.)
Shout Rockstar.
(Might as well put that number 4 on the screen.)

RPL

Although its code can sometimes be difficult to read due to stack operations, basic RPL does not provide any functionality to comment out. The only solution is then to insert strings and delete them immediately, such as:

≪ 
   SWAP - "swap the first 2 levels and subtract" DROP
≫

From 1993, comments can be added in a source code written with a text editor on a computer, starting with an @ and ending by either another @ or a newline character, before transfer to and compilation by the calculator. The compilation step removes all comments.

≪ 
   SWAP - @ swap the first 2 levels and subtract 
≫

Ruby

x = "code" # I am a comment

=begin hello
I a POD documentation comment like Perl
=end puts "code"

Run BASIC

Comments have a ' (single quote) or REM for remarks

'This is a comment
REM This is a comment
 
print "Notice comment at  the end of the line."          'This is a comment
print "Also notice this comment at the end of the line." : REM This is a comment

Rust

// A single line comment

/*
    This is a multi-line (aka block) comment

    /*
        containing nested multi-line comment
        (nesting supported since 0.9-pre https://github.com/mozilla/rust/issues/9468)
    */
*/


/// Outer single line Rustdoc comments apply to the next item.

/**
    Outer multi-line Rustdoc comments.

 *  Leading asterisk (*) in multi-line Rustdoc comments
 *  is not considered to be part of the comment text,
 *  blanks and tabs preceding the initial asterisk (*) are also stripped.
*/

fn example() {

    //! Inner single line Rustdoc comments apply to their enclosing item.

    /*!
        Inner multi-line Rustdoc comments.
        See also https://github.com/mozilla/rust/wiki/Doc-using-rustdoc
    */
}

#[doc = "Unsugared outer Rustdoc comments.
        (outer attributes are not terminated by a semi-colon)"]
fn example() {
    #[doc = "Unsugared inner Rustdoc comments.
            (inner attributes are terminated by a semi-colon)
            See also https://github.com/mozilla/rust/blob/master/doc/rust.md#attributes"];
}

SAS

/* comment */

*another comment;

* both
  may
  be
  multiline;

Sather

-- a single line comment

S-BASIC

rem S-BASIC of course allows traditional BASIC-style comments

comment
  In addition to the single-line REM statement, S-BASIC 
  also supports multiline comments using COMMENT...END.
  Note that the terminating END must be the first token on
  a line of its own.
end

comment
  When declaring a group of variables, S-BASIC allows
  a semi-colon, instead of the normal comma, as a separator,
  in which event an explanatory comment can follow the
  semi-colon and is ignored by the compiler.
end

var n   ; number of payments over life of loan
    ppy ; payments per year
    apr ; annual interest rate as a decimal
    amt ; principal amount of loan
    pmt ; amount of periodic payment
        = real

comment
   Finally, although statements in S-BASIC are normally terminated
   by an end-of-line, any logical statement can be continued on to 
   the following physical line with a backslash, in which event
   anything after the backslash is ignored and can be used for 
   a comment. 
end
 
if amt = 0 then      \ user forgot to enter a value
   print "Must specify a loan amount!"
end

Scala

// A single line comment

/* A multi-line 
   comment */

Scheme

; Basically the same as Common Lisp
; While R5RS does not provide block comments, they are defined in SRFI-30, as in Common Lisp :

#| comment
... #| nested comment
... |#
|#

; See http://srfi.schemers.org/srfi-30/srfi-30.html

Scilab

Specify a comment starting with // to the end of line

// this is a comment
i=i+1 // this is a comment

sed

# a single line comment

Seed7

# A single line comment

(* A multi-line 
    comment *)

(* In Seed7, 
(* comments can be nested. *) *)

SenseTalk

#   Hashtag is a comment
--  Dash dash is another comment
//  Slash slash is yet another comment
—   Alt/Option + Underscore creates an m-dash comment
(*  Parentheses and star is used for commenting
blocks of code (* and can be nested *) *)
set foo to true // all comments can append to statements

Set lang

> Comments start where a > (greater than symbol) starts
set a 0 > Comments may start after a Set command

SETL

print("This is not a comment"); -- This is a comment
$ For nostalgic reasons, this is also a comment.

Sidef

Single line comment

# this is commented

These may also be at the end of a line

var i = 1; # this is the comment part

Embedded comments

var distance #`{in meters} = (30 #`{meters} * 100 #`{seconds});
say distance; # prints: 3000

Multi-line comments

/*
    This is a multi-line comment
*/

Simula

The same as Algol 60:

COMMENT This is a comment for Simula 67;

And an new form:

!This is a comment for Simula 67;

Pitfall: it's not easy to comment-out parts of code:

!OutText("Dying."); !Outimage; !terminate_program;

Slate

"basically the same as smalltalk"

Smalltalk

"Comments traditionally are in double quotes."
"Multiline comments are also supported.
 Comments are saved as metadata along with the source to a method.
 A comment just after a method signature is often given to explain the
 usage of the method. The class browser may display such comments
 specially."

smart BASIC

'Single line comments are preceded by a single quote or the command REM

PRINT "Hello" 'Single line comments may follow code

PRINT "Hello" REM You can also use the command REM following code

/*
Multi-line comments
are surrounded by
mirrored slash
and asterisk 
*/

/*Multi-line comments do not have to actually have multiple lines*/

/* Spaces before or after comment bounds are optional.*/

/* A comment can also follow another comment */  'Like this

Some programmers like to do this to allow for /* Procedural comments */ followed by 'Programmer's notes.

SNOBOL4

* An asterisk in column 1 is the standard Snobol comment
* mechanism, marking the entire line as a comment. There
* are no block or multiline comments.

*               Comments may begin at
*               any position on the line.

- A hyphen in column 1 begins a control statement. 
- Unrecognized control statements are ignored and
- may also mark comment lines. Not recommended.

                   ;* The semicolon statement separator
    output = 'FOO' ;* begins a new statement. This idiom
    output = 'BAR' ;* simulates an asterisk in the first
                   ;* column, allowing end of line comments.

END

Any text after the required END label is ignored.

SNUSP

As with Brainf*** and Befunge, any character that is not part of the language is ignored and can be used as commentary, and you can add comments anywhere the instruction pointer is not expected to traverse. Reserved characters are:

Core: + - > < , . ? ! / \ $ #
Modular: @ #
Bloated: : ; & %

As a matter of convention, the characters '=' and '|' are used for spacing to indicate horizontal and vertical flow of control, respectively.

SPL

'This is single-line comment

''This is
multiline comment''

SQL

The double hyphen ( -- ) is used to include a comment on an SQL statement.

The comment appears on the same line as the statement:

SELECT * FROM mytable -- Selects all columns and rows

or before:

-- Selects all columns and rows
SELECT * FROM mytable

or after:

SELECT * FROM mytable 
-- Selects all columns and rows

SQL PL

Works with: Db2 LUW

Single line comment:

--This is a single line comment.

Multiline comment:

/* This is
a multiline
comment */

Another way to do multiline comments

(= This is
a multiline
comment =)

End of line comment:

declare myvar number; --This is an end of line comment.

Comments work the same as in SQL.

Squirrel

//this is a single line comment

#this is also a single line comment

/*
    this is a multi-line comment
*/

SSEM

The SSEM can only be programmed in pure binary, by setting front panel switches: the concepts of "text" and "source file" (both mentioned in the specification) are therefore not directly applicable to it. If binary numbers have any mnemonic or explanatory value for you, however, there is a way of including information in your program that the computer will ignore. This is a direct result of the machine's rather poor code density. Each 32-bit instruction word consists of (a) a five-bit address field giving the operand, (b) eight unused bits, (c) a three-bit instruction field giving the operation to be performed, and (d) sixteen more unused bits. If the instruction field is set to 011 Test or 111 Stop, even the address field is unused. In the case of a Sub. instruction, finally, the leftmost bit of the instruction field is disregarded: 001 and 101 both mean "subtract". We therefore have at least 24 and sometimes 25 or 29 bits in each instruction that we can, if we like, use for comments. The word

00101010010001000100100100001100

will be understood by the machine as Add 20 to CI, a normal instruction. But it also fits four comment characters into the unused bits, employing a simple five-bit encoding where A=0 and Z=25. The instruction breaks down as follows:

00101 -- address field = 20

01001 -- "comment" field = 18

000 -- three unused bits

100 -- instruction field = Add to CI

01001 -- "comment" field = 18

00100 -- "comment" field = 4

01100 -- "comment" field = 12

0 -- unused bit

Applying our simple alphabetic encoding, we see that the "spare" bits spell out 18, 18, 4, 12 = S, S, E, M.

More realistically, you can include comments when you are drafting your program using mnemonic notation and then simply leave the comments out when it comes time to toggle the program in.

Standard ML

(* This a comment
   (* containing nested comment *)
 *)

Stata

* Line comment: must be used at the beginning of a line (does not work in Mata)

// Line comment until the end of the line

/* Multiline comment

*/

SuperTalk

-- This is a comment

Swift

// this is a single line comment
/* This a block comment
   /* containing nested comment */
 */

///This is a documentation comment

/**
  This is a documentation block comment
*/

Symsyn

| This is a comment

Tcl

Tcl follows the usual scripting language rules: a comment starts at a "#" symbol, which can be placed after a command if that is terminated by a semicolon:

# comment on a line by itself. The next is a command by itself:
set var1 $value1
set var2 $value2 ; # comment that follows a line of code

The reason for the need for a semi-colon on a trailing comment is this:

"If a hash character (“#”) appears at a point where Tcl is expecting the first character of the first word of a command, then the hash character and the characters that follow it, up through the next newline, are treated as a comment and ignored. The comment character only has significance when it appears at the beginning of a command." (from the Tcl man page -- emphasis mine)

The "#" symbol has no special meaning if it is not where a command would appear -- it's just data. (Syntax highlighters often get this wrong.)

set aList {foo}
lappend aList # bar
puts $aList           ;# ==> prints "foo # bar"
puts [llength $aList] ;# ==> 3

TCL has no native multi-line comment format. However, in most circumstances, a multi-line comment can be faked by wrapping it within a block that will never be executed:

if 0 {
   Comments...
}

Tern

See Java

TI-83 BASIC

There is no 'proper' way of adding comments in TI-BASIC, however there are ways to add text to a program that will be ignored by the calculator.

One common approach is to put the comment in a string which is not stored anywhere:

:"THIS IS A COMMENT

However this will change the Ans variable.

This approach, while messier, does not affect the Ans variable:

:If 0
:THIS IS A COMMENT

TI-89 BASIC

© This is a comment. Everything from © to the end of the line is ignored.

Tiny BASIC

10 REM this is a comment
20

40 REM from above you can see that line numbers with no statement
50 REM and blank lines also are ignored

Toka

There are two ways to add comments in Toka. For full lines, or at the end of a line, the shebang is normally used:

#! Everything on this line (after the shebang to the left) will be ignored.

The shebang comments can not be used inside of functions.

In addition, Toka also accepts parenthetical comments. These are enclosed in parenthesis, and are often used for stack comments or comments inside functions.

[ ( a b -- c ) 
  ... ] is myword

In addition, parenthetical comments can span multiple lines.

( This is a
  simple, multi-line
  comment )

Since comments are provided by actual functions, the comment function must be whitespace delimited, just as with all other functions in Toka.

A final way to include text in a file is to mark a false ending with end.

... code ....
end.
Nothing following the end. will be evaluated by Toka.

TorqueScript

//This is a one line comment. There are no other commenting options in TorqueScript.

TPP

--## comments are prefixed with a long handed double paintbrush

Transd

// This is a line comment.
/* This is a single line block comment.*/
/* This is
   a multi-line
   block comment.*/

TUSCRIPT

$$ MODE TUSCRIPT
- This is a comment

TXR

@# old-style comment to end of line
@; new-style comment to end of line
@(bind a ; comment within expression
       "foo")

UNIX Shell

Works with: Bourne Shell

Works with: Korn Shell

#!/bin/sh
# A leading hash symbol begins a comment.
echo "Hello"      # Comments can appear after a statement.

# The hash symbol must be at the beginning of a word.
echo This_Is#Not_A_Comment
#Comment

C Shell

#!/bin/csh -f

# C Shell has a similar comment syntax, but only allows comments in a
# script file, not in terminal input.

echo Hello#With C Shell, the hash can also be in the middle of a word.

es

# Comments in es (extensible shell) look like those of other shells.

echo Hello#With es, the hash can also be in the middle of a word.

Unlambda

Unlambda comments start with # and extend to the end of the line:

# this is a comment.

Note that comments don't need to start at the beginning of a line, e.g.

`  # apply
.a # output "a"
i  # identity

is equivalent to

`.ai

Ursa

Comments in Ursa must be on a single line, and are denoted by a #

# this is a comment
# this is another comment

Ursala

There are lots of ways to have comments in Ursala. Here are the conventional ones.

# this is single line a comment

# this is a\
continued comment

(# this is a
multi-line comment #)

(# comments in (# this form #) can (# 
be (# arbitrarily #) #) nested #)

---- this is also a comment\
and can be continued

###
The whole rest of the file after three hashes
is a comment.

Commenting out code

There are also ways to comment out sections of code during testing. An individual item of a syntactically correct list or aggregate is commented out like this.

x = <1,## 2,3>

The 2 is ignored but 1 and 3 aren't. This also works with nested aggregates and multiple lines.

a =

<
   'to',
   ## <
      'be',
      'or'>,
   'not',
   'to',
   ## 'be'>

A syntactically correct declaration can be commented out like this.

foo = 1

##

bar = 2

baz = 3

As far as the compiler is concerned, bar is not defined, but foo and baz are. It wouldn't matter if bar took multiple lines.

Comments in compiled files

The compiler can be directed to embed comments in executable files and libraries it generates without affecting their semantics.

#comment -[
I document the source text but will also be embedded in
the output library or executable file.]-

#comment gpl'3'

The latter comment puts the standard GPL license notification in the output file.

Comments as diagnostics

A function f annotated with a crash dump wrapper expressed like this during debugging

my_input_type%C f

is equivalent to just f when changed to this in the production code.

my_input_type%Ck f

Comments as hooks

Compiling with the --depend command line option makes the compiler only scan for the #depend'ed expressions and send them to standard output.

#depend <this,expression> is (parsed)* but {
   otherwise,
   ignored}

This way, scripts and source management tools can have information passed to them from the programmer by running the compiler instead of re-implementing their own parsers.

VBA

A comment starts with a quote (') and it ends at end of line

' This is a VBA comment

VBScript

A comment starts with a quote (') and it ends at end of line

' This is a VBScript comment

Verbexx

//////////////////////////////////////////////////////////////////////////////////////////////
//
// Line Comments: 
// =============
//
@VAR v1 = 10; // Line comments start from the "//" and continue to end of the line. 
//               (normal code can appear on the same line, before the //)
//
//   Line comments can span a complete line, or start in the middle of a line.
///
//// Additional // chars and /* /*  /[  ]/ and  /] are ignored
//// Line comments can be appear to be nested, since any additional // is ignored.
///
//   Note: // can appear in strings without triggering a line comment
//         // cannot appear inside an operator (or verbname), since a line comment
//            would start
//
/////////////////////////////////////////////////////////////////////////////////////////////

/********************************************************************************************
 *
 *  Block Comments:
 *  ==============
 *
 ********************************************************************************************/
//* 
//*  These start with /* and end with the next */ .  They cannot be nested, since the first */  
//*  will end the block comment.  For example, the comment, /* /* */ */ would end after the     
//*  first */. Note that /* is ignored inside a block comment, as are   //   /[   /] and  /].
//* 
//*  Also note that something like the following will cause trouble in a block comment:
//* 
//*    /* comments                          //
//*     * more comments                     //   */  (the // does not prevent the */ from ending    
//*     * (no longer part of the comment)   //        block comment)
//*     */
//* 
//*    Note: /* can appear in strings without triggering the start of a block comment
//*          /* cannot appear inside an operator (or verbname), since a line comment will
//*             start, although */ is allowed inside an operator (verbname).  Commenting
//*             out such a verbname may cause problems.
//* 
//*    Note: Since string literals are not recognized in block comments, */ appearing
//*          in a string literal inside a block comment (perhaps commented-out code)
//*          will cause the block comment to end.  
//* 
//*    Note: It is an error to start a block comment and not end it, so that it is still
//*          in progresss when the end-of-file is reached.
//* 
//*    Block comments can appear inside lines of code:  
//* 
/*1*/@VAR/*2*/v2/*3*/=/*4*/20/*5*/;/*6*/  // a line comment can follow block comments on the 
                                           // same line

/[][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][] 
/[]                                                                                          [] 
/[]     Nestable Block Comments:                                                             []
 []     ========================                                                             []/
 []                                                                                          []/
 [][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][][]/ 

//[] 
//[]  These start with /[ and end with the next matching ]/ .  Additional occurrences
//[]  of /[ ... ]/ can appear inside a nestable block comment.  The nestable block comment    
//[]  will end only when the nest level reaches 0.  Note that /* is ignored inside a nestable     
//[]  block comment, as are  */   //  and  /].
//[]
//[]  Nestable block comments can be used to comment out blocks of code containing line 
//[]  comments or regular comments, and even balanced and well-formed nestable block comments.
//[] 
//[]    Note: /[ can appear in strings without triggering the start of a block comment.  
//[]          However, strings literals are not recognized inside a nestable block comment, so
//[]          any appearances of /[ and /] inside a string literal in a nestable block commment 
//[]          will affect the nest level, and may cause problems.
//[] 
//[]    Note: It is an error to start a nestable block comment and not end it, so that it is
//[]          still in progresss when the end of file is reached.
//[] 
//[]    Nestable block comments can appear inside lines of code:  
//[] 
/[1]/@VAR/[2]/v3/[3]/=/[4]/30/[5]/;/[6]/  // a line comment can follow nestable block comments 
                                          // on the same line

@SAY v1 v2 v3;                            // should see:   10 20 30

/]
/=================================================================================================\
|                                                                                                 |
|   /] starts a block comment that lasts until the end of the current file.  Everything after     |
|   the /] is ignored.                                                                            |
|                                                                                                 |
\=================================================================================================/

Verilog

// Single line commment.
 
/* 
   Multiple
   line
   comment.
*/

VHDL

-- Single line commment in VHDL

Vim Script

All lines starting with " are comments and will be ignored.

In most cases, " will also work after a command (i.e. the rest of the line will be ignored). But some commands like echo treat the whole line as their argument and thus will raise an error (Missing quote).

let a = 4 " A valid comment
echo "foo" " Not a comment but an argument that misses the closing quote

Visual Basic

In addition to the methods mentioned in BASIC above, it is also somewhat common to effectively comment out code by including the unwanted code inside an #If 0 ... #End If block. (This works because 0 evaluates to False in VB.) Note, however, that the IDE will complain about actual comments inside an #If 0 block unless it's also commented normally (i.e., using Rem or ').

'comment
Rem comment
#If 0
  Technically not a comment; the compiler may or may not ignore this, but the
  IDE won't. Note the somewhat odd formatting seen here; the IDE will likely
  just mark the entire line(s) as errors.
#End If

Visual Basic .NET

Visual Basic .NET uses the "'" symbol or "REM" to mark it's comments. After placing a "'", or "REM", everything in that line will be ignored.

' This is a comment
REM This is also a comment
Dim comment as string ' You can also append comments to statements
Dim comment2 as string REM You can append comments to statements

Visual Objects

// This is a comment
/* This is a comment */
* This is a comment
&& This is a comment
NOTE This is a commen

V (Vlang)

// This is a single line comment.
/*
This is a multiline comment.
   /* It can be nested. */
*/

Vorpal

# single line comment

Wart

# single-line comment

Wren

// This is a line comment.
/* This is a single line block comment.*/
/* This is
   a multi-line
   block comment.*/
/* This is/* a nested */block comment.*/

X10

All text included within the ASCII characters “/*” and “*/” is considered a comment and ignored; nested comments are not allowed.

All text from the ASCII characters “//” to the end of line is considered a comment and is ignored.

// This is a single line comment

/* 
  This comment spans
  multiple lines
*/

XLISP

; this is a comment

Xojo

// Comments are denoted by a preceding double slash or or single quote
' and continue to the end of the line. There are no multi-line comment blocks
Dim foo As Integer // Comments can also occupy the ends of code lines

XPL0

Comments are enclosed in backslash characters, but the end of a line always terminates a comment. Consequently there is no multi-line comment. For example:

Text(0, \comment\ "Hello \not a comment\ World!"); \comment

Since backslashes toggle comments on and off, it could be inconvenient to comment out a line of code that contains a comment. For example, two additional backslashes could be used to comment out this line, as shown here:

 Text(0, "Hello World");  \comment
\Text(0, "Hello World"); \\comment

However, two backslashes together comment out everything to the end of the line regardless of any backslashes the line might contain. So the first example could be commented out like this:

\\Text(0, \comment\ "Hello \not a comment\ World"); \comment

Conditional compilation can be used to effectively comment out multiple lines of code. For example:

cond false;
Text(0, "Hello World"); \comment
CrLf(0);
cond true;

XQuery

(: This is a XQuery comment :)

XSLT

<!-- Comment syntax is borrowed from XML and HTML. -->

XUL

<!-- Comment syntax is borrowed from XML and HTML. -->

Yacas

Yacas supports C++ style comments:

// This is a single line comment
/* 
  This comment spans
  multiple lines
*/

Z80 Assembly

Note: syntax depends on the assembler software but use of a semicolon is fairly standard. VASM and WinAPE use the semicolon.

 ld hl,&8000  ;This is a comment

Zig

// This is a normal comment in Zig
/// This is a documentation comment in Zig (for the following line)

zkl

x=1; // comment ala C++
x=2; # ala scripts
/* ala C, these comments are parsed (also ala C) */
/* can /* be */ nested */
#if 0
  also ala C (and parsed)
#endif
#<<<#
  "here" comment, unparsed
#<<<#

Zoea

program comments        # this program does nothing

# zoea supports single line comments starting with a '#' char

/*
  zoea also supports 
  multi line
  comments
*/

Zoea Visual

Comments

zonnon

(* this is a comment *)
(* 
   and this is a
   multiline comment
   (* with a nested comment *)
*)

Latest revision as of 13:12, 24 July 2024

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