Comparison of programming languages (syntax)

This comparison of programming languages (syntax) compares the features of language syntax (format) for over 50 various computer programming languages.

Expressions

Programming language expressions can be broadly classified in three classes:

prefix notation

• Lisp (* (+ 2 3) (expt 4 5))

infix notation

• Fortran (2 + 3) * (4 ** 5)

suffix, postfix, or Reverse Polish notation

• Forth 2 3 + 4 5 ** *

math-like notation

• TUTOR (2 + 3)(4⁵) $$ note implicit multiply operator

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.

Language	Statement separator-terminator	Secondary separator[1]
ABAP	period separated
Ada	semicolon terminated
ALGOL	semicolon separated
ALGOL 68	semicolon and comma separated[2]
AppleScript	newline terminated
AutoHotkey	newline terminated
BASIC	newline terminated	colon separated
Boo	newline terminated
C	semicolon terminates statements	comma separates expressions
C++	semicolon terminates statements	comma separates expressions
C#	semicolon terminated
COBOL	whitespace separated, sometimes period separated, optionally separated with commas and semi-colons.
Cobra	newline terminated
CoffeeScript	newline terminated
D	semicolon terminated
Eiffel	newline terminated	semicolon
Erlang	colon separated, period terminated
Falcon	newline separated
Fortran	newline terminated	semicolon
Forth	semicolons terminate word definitions
GFA BASIC	newline terminated
Go	semicolon separated (inserted by compiler)
Haskell (in do-notation)	semicolon separated
Haskell (in do-notation, when braces are omitted)	newline separated
Java	semicolon terminated
JavaScript	semicolon separated (but sometimes implicitly inserted on newlines)
Lua	whitespace separated (semicolon optional)
Mathematica	semicolon separated
MATLAB	newline terminated	semicolon or comma[3]
Object Pascal (Delphi)	semicolon separated
Objective-C	semicolon terminated
OCaml	semicolon separated
Pascal	semicolon separated
Perl	semicolon separated
Perl 6	semicolon separated
PHP	semicolon terminated
Prolog	period terminated
Python	newline terminated	semicolon
Ruby	newline terminated	semicolon
Rust	semicolon terminates statements	comma separates expressions
Scala	newline terminated (semicolon optional)	semicolon
Seed7	semicolon separated (semicolon termination is allowed)
Simula	semicolon separated
S-Lang	semicolon separated
Smalltalk	period separated
Standard ML	semicolon separated
Swift	semicolon separated (inserted by compiler)
Visual Basic	newline terminated	colon separated
Visual Basic .NET	newline terminated	colon separated
Wolfram Language	semicolon separated
Windows PowerShell	newline terminated	semicolon separated
Xojo	newline terminated
Language	Statement separator-terminator	Secondary separator[1]

Line continuation

Line continuation is generally done as part of lexical analysis: a newline normally results in a token being added to the token stream, unless line continuation is detected.

Whitespace – Languages that do not need continuations

• Ada – Lines terminate with semicolon
• C# – Lines terminate with semicolon
• Lua
• OCaml

Ampersand as last character of line

• Fortran 90, Fortran 95, Fortran 2003, Fortran 2008

Backslash as last character of line

• bash^[4] and other Unix shells
• C and C++ preprocessor
• Falcon
• Mathematica and Wolfram Language
• Python^[5]
• Ruby

Backtick as last character of line

• Windows PowerShell

Hyphen as last character of line

• SQL*Plus

Underscore as last character of line

• Autoit
• Cobra
• Visual Basic
• Xojo

Ellipsis (as three periods–not one special character)

• MATLAB: The ellipsis token need not be the last characters on the line, but any following it will be ignored.^[6] (In essence, it begins a comment that extends through (i.e. including) the first subsequent newline character. Contrast this with an inline comment, which extends until the first subsequent newline.)

Comma delimiter as last character of line

• Ruby (comment may follow delimiter)

Left bracket delimiter as last character of line

• Batch file: starting a parenthetical block can allow line continuation^[7]
• Ruby: left parenthesis, left square bracket, or left curly bracket

Operator as last object of line

• Ruby (comment may follow operator)

Backslash as first character of continued line

• Vimscript

Some form of inline comment serves as line continuation

• Turbo Assembler: \
• m4: dnl
• TeX: %

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.)
• TUTOR: Lines starting with a tab (after any indentation required by the context) continue the previous command.

[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.

Libraries

To import a library is a way to read external, possibly compiled, routines, programs or packages. Imports can be classified by level (module, package, class, procedure,...) and by syntax (directive name, attributes,...)

File import

• ASP: #include file="filename"
• AutoIt, C, C++: #include "filename", #include <filename>
• COBOL: COPY filename.
• Falcon: load "filename"
• Fortran: include 'filename'
• Lua: require("filename")
• Mathematica and Wolfram Language: Import["filename"]
• MATLAB: addpath(directory)^[8]
• Objective-C: #import "filename", #import <filename>
• Perl: require "filename";
• PHP: include "filename";, require "filename";
• R: source(""filename"")
• Rust: include!( "filename");

Package import

• Ada: with package
• C, C++: #include filename
• Cobra: use Package.Name
• D: import package.module;, import altname = package.module;
• Falcon: load module, load module.submodule
• Fortran 90+: use module, use module, only : identifier
• Go: import altname "package/name"
• Haskell: import Module, import qualified Module as M
• Java, MATLAB: import package.*
• Lua: require("modname")
• Mathematica and Wolfram Language: <<name
• Oberon: IMPORT module
• Objective-C: @import module;
• Pascal: uses unit
• Perl: use Module;, use Module qw(import options);
• Python: import module, from module import *
• Rust: mod modname;, #[path = "filename"] mod altname;, extern crate libname;, extern crate libname as altname;
• R: library(""package"")
• Scala: import package._, import package
• Swift: import module

Class import

• Falcon: import class
• Java, MATLAB: import package.class
• Python: from module import class
• Scala: import package.class, import package.{ class1 => alternativeName, 'class2 }, import package._

Procedure/function import

• D: import package.module : symbol;, import package.module : altsymbolname = symbol;
• Haskell: import Module (function)
• MATLAB: import package.function
• Perl: use Module ('symbol');
• Python: from module import function
• Rust: use module::submodule::symbol;, use module::submodule::{symbol1, symbol2};, use module::submodule::symbol as altname;
• Scala: import package.class.function, import package.class.{ function => alternativeName, otherFunction }

The above statements can also be classified by whether they are a syntactic convenience (allowing things to be referred to by a shorter name, but they can still be referred to by some fully qualified name without import), or whether they are actually required to access the code (without which it is impossible to access the code, even with fully qualified names).

Syntactic convenience

• Java: import package.*, import package.class
• OCaml: open module

Required to access code

• Go: import altname "package/name"
• Python: import module

Blocks

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 (a.k.a. curly brackets) { ... }

• Curly bracket programming languages: C, C++, Objective-C, Go, Java, JavaScript, ECMAScript, C#, D, Perl, PHP (for & loop loops, or pass a block as argument), Rust, Scala, S-Lang, Swift, Windows PowerShell, Haskell (in do-notation)

Parentheses ( ... )

• OCaml, Standard ML

Brackets [ ... ]

• Smalltalk (blocks are first class objects. a.k.a. closures)

begin ... end

• Ada, ALGOL, Pascal, Ruby (for, do/while & do/until loops), OCaml, Simula, Erlang.

do ... done

• Visual Basic, Fortran, TUTOR (with mandatory indenting of block body), Visual Prolog

do ... end

• Lua, Ruby (pass blocks as arguments, for loop), Seed7 (encloses loop bodies between do and end)

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

• Bash (for & while loops), Ruby (if, while, until, def, class, module statements), OCaml (for & while loops), MATLAB (if & switch conditionals, for & while loops, try clause, package, classdef, properties, methods, events, & function blocks), Lua (then / else & function)

(begin ...)

• Scheme

(progn ...)

• Lisp

(do ...)

• Clojure

Indentation

• Off-side rule languages: Cobra, CoffeeScript, F#, Haskell (in do-notation when braces are omitted), occam, Python
• Free-form languages: most descendants from ALGOL (including C, Pascal, and Perl); Lisp languages

Others

• Ada, Visual Basic, Seed7: if ... end if
• Bash, sh, and ksh: if ... fi, do ... done, case ... esac;
• ALGOL 68: begin ... end, ( ... ), if ... fi, do ... od
• Lua, Pascal, Modula-2, Seed7: repeat ... until
• COBOL: IF ... END-IF, PERFORM ... END-PERFORM, etc. for statements; ... . for sentences.

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:

Symbol	Languages
C	Fortran 77 and earlier; the 'C' must be in column 1 of a line to indicate a comment.
REM, ::, :	BASIC, COMMAND.COM, cmd.exe, batch files
NB.	J; from the (historically) common abbreviation Nota bene, the Latin for "note well".
⍝	APL; the mnemonic is the glyph (jot overstruck with shoe-down) resembles a desk lamp, and hence "illuminates" the foregoing.
#	Bourne shell and other UNIX shells, Cobra, Perl, Python, Ruby, Seed7, Windows PowerShell, PHP, R, Make, Maple, Nimrod[9]
%	TeX, Prolog, MATLAB,[10] Erlang, S-Lang, Visual Prolog
//	ActionScript, C (C99), C++, C#, D, Go, Java, JavaScript, Object Pascal (Delphi), Objective-C, PHP, Rust, Scala, SASS, Swift, Xojo
'	Monkey, Visual Basic, VBScript Small Basic, Gambas, Xojo
!	Fortran, Basic Plus, Inform
;	AutoHotkey, AutoIt, Lisp, Common Lisp, Clojure, Rebol, Scheme, many assemblers
--	Euphoria, Haskell, SQL, Ada, AppleScript, Eiffel, Lua, VHDL, SGML
*	COBOL (if fixed-form and * in column 7), PAW, many assemblers, Fortran (if fixed-form and * in column 1)
||	Curl
"	Vimscript
\	Forth
*>	COBOL

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:

Symbol	Languages
¢ ~ ¢, # ~ #,co ~ co, comment ~ comment	ALGOL 68[11][12]
/* ~ */	ActionScript, AutoHotkey, C, C++, C#, D,[13] Go, Java, JavaScript, Objective-C, PHP, PL/I, Rust (can be nested), Scala (can be nested), SASS, SQL, Swift, Visual Prolog, CSS
#cs ~ #ce	AutoIt[14]
/+ ~ +/	D (can be nested)[13]
/# ~ #/	Cobra (can be nested)
<# ~ #>	Powershell
=begin ~ =cut	Perl
#`( ~ )	Perl6 (bracketing characters can be (), <>, {}, [], any Unicode characters with BiDi mirrorings, or Unicode characters with Ps/Pe/Pi/Pf properties)
=begin ~ =end	Ruby
#<TAG> ~ #</TAG>, #stop ~ EOF, #iffalse ~ #endif, #ifntrue ~ #endif, #if false ~ #endif, #if !true ~ #endif	S-Lang[15]
{- ~ -}	Haskell (can be nested)
(* ~ *)	Object Pascal (Delphi), ML, Mathematica, Pascal, Seed7, Applescript, OCaml (can be nested), Standard ML (can be nested), Maple, Newspeak
{ ~ }	Object Pascal (Delphi), Pascal
|# ~ #|	Curl
%{ ~ %}	MATLAB[10] (the symbols must be in a separate line)
#| ~ |#	Lisp, Scheme, Racket (can be nested in all three).
--[[</code> ~ <code>]], --[=[ ~ ]=]	Lua (the former form can be nested, but only within the latter, which can't be nested)
" ~ "	Smalltalk
(comment ~ )	Clojure

Unique variants

Fortran

• Indenting 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 often 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 inline comments, using the ! character as the comment delimiter.

COBOL

• In fixed format code, line indentation is significant. Columns 1–6 and columns from 73 onwards are ignored. If a * or / is in column 7, then that line is a comment. Until COBOL 2002, if a D or d was in column 7, it would define a "debugging line" which would be ignored unless the compiler was instructed to compile it.

Cobra

• Cobra supports block comments with "/# ... #/" which is like the "/* ... */" often found in C-based languages, but with two differences. The # character is reused from the single-line comment form "# ...", and the block comments can be nested which is convenient for commenting out large blocks of code.

Curl

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

Lua

• Like raw strings, there can be any number of equals signs between the square brackets, provided both the opening and closing tags have a matching number of equals signs; this allows nesting as long as nested block comments/raw strings use a different number of equals signs than their enclosing comment: --[[comment --[=[ nested comment ]=] ]]. Lua discards the first newline (if present) that directly follows the opening tag.

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 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.

Scheme and Racket

• The next complete syntactic component (s-expression) can be commented out with #; .

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), 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.

Language	In-line comment	Block comment
Ada, Eiffel, Euphoria, Occam, SPARK, ANSI SQL, and VHDL	-- InlineComment
ALGOL 60		comment BlockComment;
ALGOL 68		¢ BlockComment ¢ comment BlockComment comment co BlockComment co # BlockComment # £ BlockComment £
AppleScript	-- InlineComment	(* BlockComment *)
Assembly language (varies)	; InlineComment   one example (most assembly languages use line comments only)
AutoHotkey	; InlineComment	/* BlockComment */
AWK, Bash, Bourne shell, C shell, Maple, R, Tcl, and Windows PowerShell	# InlineComment	<# BlockComment #>
BASIC (various dialects):	'InlineComment (not all dialects) REM InlineComment
C (K&R, ANSI/C89/C90), CHILL, PL/I, and REXX		/* BlockComment */
C (C99), C++, Go, and JavaScript	// InlineComment	/* BlockComment */
C#	// InlineComment /// InlineComment (XML documentation comment)	/* BlockComment */ /** BlockComment */ (XML documentation comment)
COBOL	InlineComment (when * or / is in column 7) *> InlineComment
Curl	|| InlineComment	|# BlockComment #| |foo# BlockComment #|
Cobra	# InlineComment	/# BlockComment #/ (nestable)
D	// InlineComment /// Documentation InlineComment (ddoc comments)	/* BlockComment */ /** Documentation BlockComment */ (ddoc comments) /+ BlockComment +/ (nestable) /++ Documentation BlockComment +/ (nestable, ddoc comments)
DCL	$! InlineComment
ECMAScript (JavaScript, ActionScript, etc.)	// InlineComment	/* BlockComment */
Forth	\ InlineComment	( BlockComment ) (single line only) ( before -- after ) stack comment convention
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)
Haskell	-- InlineComment	{- BlockComment -}
Java	// InlineComment	/* BlockComment */ /** BlockComment */ (Javadoc documentation comment)
Lisp and Scheme	; InlineComment	#| BlockComment |#
Lua	-- InlineComment	--[==[ BlockComment]==] (variable number of = signs)
Maple	# InlineComment	(* BlockComment *)
Mathematica		(* BlockComment *)
Matlab	% InlineComment	%{ BlockComment (nestable) %} Note: Both percent–bracket symbols must be the only non-whitespace characters on their respective lines.
Object Pascal (Delphi)	// InlineComment	(* BlockComment *) { BlockComment }
OCaml		(* BlockComment (* nestable *) *)
Pascal, Modula-2, Modula-3, Oberon, and ML:		(* BlockComment *)
Perl and Ruby	# InlineComment	=begin BlockComment =cut (=end in Ruby) (POD documentation comment) __END__ Comments after end of code
PHP	# InlineComment // InlineComment	/* BlockComment */ /** Documentation BlockComment */ (PHP Doc comments)
PILOT	R:InlineComment
PL/SQL and TSQL	-- InlineComment	/* BlockComment */
Python	# InlineComment	''' BlockComment ''' """ BlockComment """ (Documentation string when first line of module, class, method, or function)
Rust	// InlineComment /// InlineComment ("Outer" rustdoc comment) //! InlineComment ("Inner" rustdoc comment)	/* BlockComment */ (nestable) /** BlockComment */ ("Outer" rustdoc comment) /*! BlockComment */ ("Inner" rustdoc comment)
SAS		* BlockComment; /* BlockComment */
Seed7	# InlineComment	(* BlockComment *)
Simula		comment BlockComment; ! BlockComment;
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	% InlineComment	/* BlockComment */
Wolfram Language		(* BlockComment *)
Xojo	' InlineComment // InlineComment rem InlineComment

See also

• Curly bracket programming languages, a broad family of programming language syntaxes
• PHP syntax and semantics
• C syntax
• C++ syntax
• Java syntax
• Javascript syntax
• Python syntax and semantics

References

1. For multiple statements on one line
2. Three different kinds of clauses, each separates phrases and the units differently:
   • 1. serial-clause using go-on-token (viz. semicolon): begin a; b; c end – units are executed in order.
     2. collateral-clause using and-also-token (viz. “,”): begin a, b, c end – order of execution is to be optimised by the compiler.
     3. parallel-clause using and-also-token (viz. “,”): par begin a, b, c end – units must be run in parallel threads.
3. semicolon – result of receding statement hidden, comma – result displayed
4. Bash Reference Manual, 3.1.2.1 Escape Character
5. Python Documentation, 2. Lexical analysis: 2.1.5. Explicit line joining
6. Mathworks.com
7. http://ss64.com/nt/syntax-brackets.html
8. For an M-file (MATLAB source) to be accessible by name, its parent directory must be in the search path (or current directory).
9. http://nimrod-lang.org/manual.html#comments
10. "Mathworks.com". Retrieved 25 June 2013.
11. "Algol68_revised_report-AB.pdf on PDF page 61-62, original document page 121-122" (PDF). Retrieved 27 May 2014.
12. "HTML Version of the Algol68 Revised Report AB". Retrieved 27 May 2014.
13. "DLang.org, Lexical". Retrieved 27 May 2014.
14. "AutoItScript.com Keyword Reference, #comments-start". Retrieved 27 May 2014.
15. "slang-2.2.4/src/slprepr.c - line 43 to 113". Retrieved 28 May 2014.