Comparison of programming languages (syntax)

Statements

Programming language statements typically have conventions for:

• statement separators;
• statement terminators; and
• line continuation

A statement separator is used to demarcate boundaries between two separate statements. A statement terminator is used to demarcate the end of an individual statement. Line continuation is a convention in languages where the newline character could potentially be misinterpreted as a statement terminator. In such languages, it allows a single statement to span more than just one line.

Statement terminators

Semicolon terminated:

• C, C++, C#, Objective-C, D, Java, PHP, Javascript (semicolon optional), S-Lang

Newline terminated:

• AutoHotkey, BASIC, GFA BASIC, Visual Basic, Visual Basic .NET, Fortran, Ruby, Python, Windows PowerShell

Period terminated:

• Smalltalk, Prolog, Erlang

Statement separators

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Semicolon separated:

• ALGOL, Pascal, Object Pascal (Delphi), Javascript, Windows PowerShell, Perl, S-Lang, OCaml, Haskell (in do-notation)
• (Secondary) FORTRAN^[1], Eiffel^[1], Python^[1]

Period separated:

• Cobol, ABAP

Colon separated:

• (Secondary) BASIC^[1]

Whitespace separated

• Forth^[1], lua

Newline separated:

• Haskell (in do-notation, when braces are omitted)

Line continuation

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Backslash as last character of line

• C and C++ preprocessor
• Python
• Ruby

Ampersand as last character of line

• Fortran 90/Fortran 95

Backtick as last character of line

• Windows PowerShell

Underscore as last character of line

• Visual Basic
• Autoit

Some form of inline comment serves as line continuation

• Turbo Assembler: \
• m4: dnl

Character position

• Fortran 77: A non-comment line is a continuation of the previous non-comment line if any non-space character appears in column 6. Comment lines cannot be continued.
• Cobol: String constants may be continued by not ending the original string in a PICTURE clause with ', then inserting a - in column 7 (same position as the * for comment is used.)

[End and Begin] using normal quotes

• C and C++ preprocessor: The string is ended normally and continues by starting with a quote on the next line.

Blocks

Please help improve this section by expanding it. Further information might be found on the talk page. (Nov 2008)

A block is a notation for a group of two or more statements, expressions or other units of code that are related in such a way as to comprise a whole.

Braces (aka Curly brackets) { }:

• Curly bracket programming languages: C, C++, Java, JavaScript, ECMAScript, C#, D, Perl, PHP, S-Lang, Windows PowerShell, Haskell (in do-notation)

Indentation

• Off-side rule languages: Python, Haskell (in do-notation when braces are omitted)

begin ... end:

• Pascal, OCaml

(begin ...):

• Scheme

(progn ...):

• Lisp

Parentheses

• OCaml

X ... EndX (e.g. if ... end if):

• Visual Basic, Ada, C preprocessor, Fortran, Bash (if .. fi)

X ... end (e.g. if ... end):

• Ruby

do ... done:

• Bash (for & while loops), OCaml (for & while loops)

Comments

Comments can be classified by:

• style (inline/block)
• parse rules (ignored/interpolated/stored in memory)
• recursivity (nestable/non-nestable)
• uses (docstrings/throwaway comments/other)

Inline comments

Inline comments are generally those that use a newline character to indicate the end of a comment, and an arbitrary delimiter or sequence of tokens to indicate the beginning of a comment.

Examples:

Block comments

Block comments are generally those that use a delimiter to indicate the beginning of a comment, and another delimiter to indicate the end of a comment. In this context, whitespace and newline characters are not counted as delimiters.

Examples:

Unique variants

Fortran

• The indentation of lines in FORTRAN 66/77 is significant. The actual statement is in columns 7 through 72 of a line. Any non-space character in column 6 indicates that this line is a continuation of the previous line. A 'C' in column 1 indicates that this entire line is a comment. Columns 1 though 5 may contain a number which serves as a label. Columns 73 though 80 are ignored and may be used for comments; in the days of punched cards these columns contained a sequence number so that the deck of cards could be sorted into the correct order if someone accidentally dropped the cards. Fortran 90 removed the need for the indentation rule and added traditional inline comments, using the ! character as the comment delimiter.

Curl

• Curl supports block comments with user-defined tags as in |foo# ... #foo|

Perl

• Block comments in Perl are considered part of the documentation, and are given the name Plain Old Documentation (POD). Technically, Perl does not have a convention for including block comments in source code, but POD is routinely used as a workaround.

PHP

• PHP supports standard C/C++ style comments, but also supports Perl style as well.

Python

• The use of the triple-(double)quotes although sometimes used to comment-out lines of source, does not actually form a comment. The enclosed text becomes a string, usually a string statement. Python usually ignores a lone string as a statement (except when a string is the first statement in the body of a module, class or function; see docstring).

Ruby

• As with Python and Perl, Ruby has no specific block-comment syntax. However, like Perl, documentation blocks can be used as block comments as they are ignored by the interpreter.

S-Lang

• The region of lines enclosed by the #<tag> and #</tag> delimiters are ignored by the interpreter. The tag name can be any sequence of alphanumeric characters that may be used to indicate how the enclosed block is to be deciphered. For example, #<latex> could indicate the start of a block of LaTeX formatted documentation.

Esoteric languages

• Many esoteric programming languages follow the convention that any text not executed by the instruction pointer (e.g., Befunge) or otherwise assigned a meaning (e.g., Brainfuck, ETA) is considered a "comment".

Comment comparison

There is a wide variety of syntax styles for declaring comments in source code. BlockComment in italics is used here to indicate block comment style. InlineComment in italics is used here to indicate inline comment style.

• Ada, Eiffel, Euphoria, Lua, Occam, SPARK, ANSI SQL, ToolBook OpenScript, and VHDL:
  • -- InlineComment
• ALGOL 60:
  • comment BlockComment;
• ALGOL 68:
  • ¢ BlockComment ¢
  • comment BlockComment comment
  • co BlockComment co
  • # BlockComment #
  • £ BlockComment £
• AppleScript:
  • (* BlockComment *)
  • -- InlineComment
• Assembly language: (varies)
  • ; InlineComment   one example (most assembly languages use line comments only)
• AutoHotkey:
  • ; InlineComment
  • /* BlockComment */
• AWK, Bash, Bourne shell, C shell, Maple, Python, R, Tcl, and Windows PowerShell:
  • # InlineComment
• BASIC (various dialects):
  • 'InlineComment (not all dialects)
  • REM InlineComment
• C (K&R, ANSI/C89/C90), CHILL, CSS, PL/I, and REXX:
  • /* BlockComment */
• C (C99), C++, and JavaScript:
  • /* BlockComment */
  • // InlineComment
• C#
  • /* BlockComment */
  • /** BlockComment */ (XML documentation comment)
  • // InlineComment
  • /// InlineComment (XML documentation comment)
• Cobol:
  • * InlineComment when * is in column 7
• Curl:
  • || InlineComment</code?
  • |# BlockComment #|
  • |foo# BlockComment #foo|
• D:
  • /* BlockComment */
  • // InlineComment
  • /+ BlockComment +/ (nestable)
• DCL:
  • $! InlineComment
• ECMAScript (JavaScript, ActionScript, etc):
  • /* BlockComment */
  • // InlineComment
• Forth:
  • ( BlockComment )
  • \ InlineComment
• FORTRAN 66/77:
  • C InlineComment (the letter 'C' in the first column makes the entire line a comment).
• Fortran 90:
  • ! InlineComment (all characters on the line, from the exclamation mark onwards, are comments)
• HTML (see SGML below)
• Java:
  • // InlineComment
  • /* BlockComment */
  • /** BlockComment */ (Javadoc documentation comment)
• Lisp and Scheme
  • #| BlockComment |#
  • ; InlineComment
• Maple:
  • # InlineComment
• Mathematica:
  • % (* BlockComment *)
• Matlab:
  • % BlockComment;
  • %{
Use this to comment out multiple lines without placing a "%" in front of every single one.
Nothing besides %{ must appear on that line
%}

• Object Pascal (Delphi):
  • (* BlockComment *)
  • { BlockComment }
  • // InlineComment
• Pascal, Modula-2, Modula-3, Oberon, and ML:
  • (* BlockComment *) (OCaml comments are nestable)
• Perl and Ruby:
  • # InlineComment
  • =begin
BlockComment
=cut (POD documentation comment)
  • __END__
Comments after end of code
• PHP:
  • # InlineComment
  • // InlineComment
  • /* BlockComment */
• PILOT:
  • R:InlineComment
• PL/SQL and TSQL:
  • /* BlockComment */
  • -- InlineComment
• REALbasic:
  • ' InlineComment
  • // InlineComment
  • rem InlineComment
• SAS:
  • * BlockComment;
  • /* BlockComment */
• Seed7:
  • (* BlockComment *)
  • # InlineComment
• SGML, including HTML:

  A comment declaration starts with <!, followed by zero or more comments, followed by >. A comment starts and ends with --, and does not contain any occurrence of --. Valid examples are:

  • <!-- BlockComment -- -- BlockComment -->,
  • <!------ BlockComment -->, or
  • <!>.
• Smalltalk:
  • "BlockComment"
• Smarty:
  • {* BlockComment *}
• Standard ML:
  • (* BlockComment *)
• TeX, LaTeX, PostScript, Erlang, and S-Lang:
  • % InlineComment
• Texinfo:
  • @c InlineComment
  • @comment InlineComment
• TUTOR:
  • * InlineComment
  • command $$ InlineComment
• Visual Basic:
  • ' InlineComment
  • Rem InlineComment
• Visual Basic .NET
  • ' InlineComment
  • ''' InlineComment (XML documentation comment)
  • Rem InlineComment
• Visual Prolog:
  • /* BlockComment */
  • % InlineComment
• XML, including XHTML:
  • <!--BlockComment--> (comment must not contain -- and must not start or end with single -)

References