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Comparison of programming languages (syntax)This is a comparison of programming language syntax. ExpressionsProgramming language expressions can be broadly classified in three classes: prefix notation - Lisp (* (+ 2 3) (expt 4 5))
infix notation - Fortran (2 + 3) * (4 ** 5)
- TUTOR (2 + 3)(45) $$ note implicit multiply operator
suffix, postfix, or Reverse Polish notation StatementsProgramming 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. |
| 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 | | Boo | newline terminated | | C | semicolon terminates statements | comma separates expressions | | C++ | semicolon terminates statements | comma separates expressions | | C# | semicolon terminated | | COBOL | period separated | | Cobra | newline terminated | | D | semicolon terminated | | Eiffel | newline terminated | semicolon | | Erlang | colon separated, period terminated | | Falcon | newline separated | | Fortran | newline terminated | semicolon | | Forth | ? | whitespace | | 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 | | PHP | semicolon terminated | | Prolog | period terminated | | Python | newline terminated | semicolon | | Ruby | newline terminated | semicolon | | 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 | | Visual Basic | newline terminated | | Visual Basic .NET | newline terminated | | Windows PowerShell | newline terminated | semicolon separated | | Language | Statement separator/terminator | Secondary separator[1] |
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Line continuationWhitespace - Languages that do not need continuations - Ada Lines terminate with semicolon
- C# Lines terminate with semicolon
- Lua
- OCaml
Ampersand as last character of line Backslash as last character of line Backtick as last character of line Hyphen as last character of line Left parenthesis 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.[5] (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.)
Some form of inline comment serves as line continuation 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.
LibrariesTo 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> - Falcon:
load "filename" - Fortran:
include 'filename' - Lua:
require("filename") - MATLAB:
addpath(directory)[6] - Perl:
require "filename"; - PHP:
include "filename";, require "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:
<<name - Oberon:
IMPORT module - Pascal:
uses unit - Perl:
use Module; - Python:
import module, from module import * - Scala:
import package._, import package
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 - 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
BlocksA 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++, Objective-C, Go, Java, JavaScript, ECMAScript, C#, D, Perl, PHP (
for & loop loops, or pass a block as argument), Scala, S-Lang, Windows PowerShell, Haskell (in do-notation)
Parentheses ( ... ) Brackets [ ... ] - Smalltalk (blocks are first class objects. aka closures)
begin ... end:
do ... done:
do ... end
- Lua, Ruby (pass blocks as arguments,
for loop)
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 ...): (progn ...): (do ...): Indentation Others - Bash, sh, and ksh:
if ... fi, do ... done, case ... esac; - ALGOL 68:
begin ... end, ( ... ), if ... fi, do ... od - Lua:
repeat ... until - COBOL:
IF ... END-IF, PERFORM ... END-PERFORM
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 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 | 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. | # | bash, Cobra, Perl, Python, Ruby, Windows PowerShell, PHP, Maple | % | TeX, Prolog, MATLAB,[7] Erlang, S-Lang, Visual Prolog | // | ActionScript, C (C99), C++, C#, D, Go, Java, JavaScript, Object Pascal (Delphi), Objective-C, PHP, Scala, SASS | ' | Visual Basic, VBScript, RealBasic | ! | Fortran, Basic Plus, Inform | ; | AutoHotkey, AutoIt, Lisp, Common Lisp, Clojure, Rebol, Scheme, many assemblers | -- | Euphoria, Haskell, SQL, Ada, AppleScript, Eiffel, Lua, VHDL, SGML | * | COBOL, PAW, many assemblers | || | Curl | " | Vimscript | \ | Forth | :: | Batch file[8] |
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 | /* */ | ActionScript, AutoHotkey, C, C++, C#, D, Go, Java, JavaScript, Objective-C, PHP, PL/I, Scala (can be nested), SASS, SQL, Visual Prolog, CSS | #cs #ce | AutoIt | /+ +/ | D (can be nested) | /# #/ | Cobra (can be nested) | <# #> | Powershell | =begin =cut | Perl | =begin =end | Ruby | #<tag></code> <code>#</tag> | S-Lang | {- -} | Haskell (can be nested) | (* *) | Object Pascal (Delphi), ML, Mathematica, Pascal, Applescript, OCaml (can be nested), Standard ML (can be nested), Maple | { } | Object Pascal (Delphi), Pascal | |# #| | Curl | %{ %} | MATLAB[7] | #| |# | Lisp, Scheme, Racket (can be nested in all three). | --[[ ]] | Lua | " " | Smalltalk | (comment ...) | Clojure |
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 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.
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 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, ToolBook OpenScript, 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 * is in column 7) | | | 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 *) (OCaml comments are nestable) | | Perl and Ruby | # InlineComment | =begin
BlockComment
=cut (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 """
(Documentation string when first line of module, class, method, or function) | | REALbasic | ' InlineComment
// InlineComment
rem InlineComment | | | 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 */ |
See also References- ^ a b 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
- ^ http://ss64.com/nt/syntax-brackets.html
- ^ Mathworks.com
- ^ For an M-file (MATLAB source) to be accessible by name, its parent directory must be in the search path (or current directory).
- ^ a b Mathworks.com
- ^ SS64.com
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