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 into four syntax structures:
- 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] | |
APL | ⋄ separated | |
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) | newline separated | |
Haskell (in do-notation, when braces are used) | semicolon separated | |
Java | semicolon terminated | |
JavaScript | semicolon separated (but sometimes implicitly inserted on newlines) | |
Kotlin | 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 | |
PowerShell | newline terminated | semicolon separated |
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 | |
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
- Ampersand as last character of line
- 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
- Hyphen as last character of line
- Underscore as last character of line
- 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
- 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, kotlin:
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, kotlin:
import package.class
- PHP:
use Namespace\ClassName;
,use Namespace\ClassName as AliasName;
- 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');
- PHP:
use function Namespace\function_name;
,use Namespace\function_name as function_alias_name;
- 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 }
- Constant import
- PHP:
use const Namespace\CONST_NAME;
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
- Required to access code
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
(
...)
- Brackets
[
...]
- Smalltalk (blocks are first class objects. a.k.a. closures)
begin
...end
do
...done
- Bash (
for
&while
loops), Visual Basic, Fortran, TUTOR (with mandatory indenting of block body), Visual Prolog
do
...end
- X ...
end
(e.g.if
...end
):
- 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
...)
- (progn ...)
- (
do
...)
- 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, Elixir, S-Lang, Visual Prolog |
// |
ActionScript, C (C99), C++, C#, D, Go, Java, JavaScript, kotlin, 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, kotlin, 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 aD
ord
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 5
- Block comments in Perl 5 are considered part of the documentation, and are given the name Plain Old Documentation (POD). Technically, Perl 5 does not have a convention for including block comments in source code, but POD is routinely used as a workaround. This has been addressed in Perl 6, which uses
#`(...)
to denote block comments.[16] Perl 6 actually allows the use of any "right" and "left" paired brackets after#`
(i.e.#`(...)
,#`[...]
,#`{...}
,#`<...>
, and even the more complicated#`{{...}}
are all valid block comments). Brackets are also allowed to be nested inside comments (i.e.#`{ a { b } c }
goes to the last closing brace).
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
#;
.
ABAP
ABAP supports two different kinds of comments. If the first character of a line, including indentation, is an asterisk (*
) the whole line is considered as a comment, while a single double quote ("
) begins an in-line commet which acts until the end of the line. ABAP comments are not possible between the statements EXEC SQL
and ENDEXEC
because Native SQL has other usages for these characters. In the most SQL dialects the double dash (--
) can be used instead.
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 ¢
| |
APL | ⍝ InlineComment |
|
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)
|
|
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)
|
|
Curl | || InlineComment |
|# BlockComment #|
|
Cobra | # InlineComment |
/# BlockComment #/ (nestable) |
D | // InlineComment /// Documentation InlineComment (ddoc comments) |
/* BlockComment */ /** Documentation BlockComment */ (ddoc comments)
|
DCL | $! InlineComment |
|
ECMAScript (JavaScript, ActionScript, etc.) | // InlineComment |
/* BlockComment */ |
Forth | \ InlineComment |
( BlockComment ) (single line as well as multiline)
|
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 */
|
Lisp and Scheme | ; InlineComment |
#| BlockComment |# |
Lua | -- InlineComment |
--[==[ BlockComment]==] (variable number of = signs) |
Maple | # InlineComment |
(* BlockComment *) |
Mathematica | (* BlockComment *) | |
Matlab | % InlineComment |
%{ 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 (=end in Ruby) (POD documentation comment)
|
Perl 6 | # InlineComment |
#`{
|
PHP | # InlineComment // InlineComment |
/* BlockComment */ /** Documentation BlockComment */ (PHP Doc comments) |
PILOT | R:InlineComment |
|
PLZ/SYS | ! BlockComment ! | |
PL/SQL and TSQL | -- InlineComment |
/* BlockComment */ |
Python | # InlineComment |
''' BlockComment ''' (Documentation string when first line of module, class, method, or function) |
Rust | // InlineComment
|
/* BlockComment */ (nestable)
|
SAS | * BlockComment; /* BlockComment */ | |
Seed7 | # InlineComment |
(* BlockComment *) |
Simula | comment BlockComment; ! BlockComment; | |
Smalltalk | "BlockComment" | |
Smarty | {* BlockComment *} | |
Standard ML | (* BlockComment *) | |
TeX, LaTeX, PostScript, Erlang, Elixir and S-Lang | % InlineComment |
|
Texinfo | @c InlineComment
|
|
TUTOR | * InlineComment command $$ InlineComment |
|
Visual Basic | ' InlineComment Rem InlineComment |
|
Visual Basic .NET | ' 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 2 For multiple statements on one line
- ↑ Three different kinds of clauses, each separates phrases and the units differently:
- serial-clause using go-on-token (viz. semicolon): begin a; b; c end – units are executed in order.
- collateral-clause using and-also-token (viz. “,”): begin a, b, c end – order of execution is to be optimised by the compiler.
- parallel-clause using and-also-token (viz. “,”): par begin a, b, c end – units must be run in parallel threads.
- ↑ semicolon – result of receding statement hidden, comma – result displayed
- ↑ Bash Reference Manual, 3.1.2.1 Escape Character
- ↑ Python Documentation, 2. Lexical analysis: 2.1.5. Explicit line joining
- ↑ Mathworks.com Archived 7 February 2010 at the Wayback Machine.
- ↑ https://ss64.com/nt/syntax-brackets.html
- ↑ For an M-file (MATLAB source) to be accessible by name, its parent directory must be in the search path (or current directory).
- ↑ http://nimrod-lang.org/manual.html#comments
- 1 2 "Mathworks.com". Retrieved 25 June 2013.
- ↑ "Algol68_revised_report-AB.pdf on PDF page 61-62, original document page 121-122" (PDF). Retrieved 27 May 2014.
- ↑ "HTML Version of the Algol68 Revised Report AB". Archived from the original on 17 March 2013. Retrieved 27 May 2014.
- 1 2 "DLang.org, Lexical". Retrieved 27 May 2014.
- ↑ "AutoItScript.com Keyword Reference, #comments-start". Retrieved 27 May 2014.
- ↑ "slang-2.2.4/src/slprepr.c - line 43 to 113". Retrieved 28 May 2014.
- ↑ "Perl 6 Documentation (Syntax)". docs.perl6.org. Comments. Retrieved 2017-04-05.
- ↑ "Perl 6 POD Comments".
- ↑ "Perl 6 POD (Abbreviated Blocks)".