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Comparison of programming languages (syntax)

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Comparison of
programming languages
Comparison of individual
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)
  • TUTOR (2 + 3)(45) $$ note implicit multiply operator

suffix, postfix, or Reverse Polish notation

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 separated
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 ? semicolon
Erlang colon separated, period terminated
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)
MATLAB newline terminated semicolon or comma[3]
OCaml semicolon separated
Object Pascal (Delphi) semicolon separated
Objective-C semicolon terminated
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
Simula semicolon separated
S-Lang semicolon separated
Smalltalk period separated
Visual Basic newline terminated
Visual Basic .NET newline terminated
Windows PowerShell newline terminated semicolon separated
Language Statement separator/terminator Secondary separator[1]

Line continuation

Whitespace - Languages that do not need continuations

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

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:[5] 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.)

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.

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"
  • C, C++: #include "filename", #include <filename>
  • Lua: dofile("filename"), loadfile("filename")
  • MATLAB: addpath(directory)[7]
  • Perl: require "filename";, PHP include filename

Package import

  • Ada: with package
  • C, C++: #include filename
  • Cobra: use Package.Name
  • D: import package.module;, import altname = package.module;
  • Go: import altname "package/name"
  • Java, MATLAB: import package.*
  • Lua: require("modname")
  • Oberon: IMPORT module
  • Pascal: uses unit
  • Perl: use Module;
  • Python: import module, from module import *
  • Scala: import package._, import package

Class import

  • 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;
  • MATLAB: import package.function, Perl: use Module ('symbol');
  • Python: from module import function
  • Scala: import package.class.function, import package.class.{ function => alternativeName, otherFunction }

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 (aka Curly brackets) { }:

Parentheses

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 ...):

Indentation

Others

  • Bash: if ~ fi, do ~ done, case ~ esac;
  • ALGOL 68: begin ~ end, ( ~ ), if ~ fi, do ~ od
  • Lua: repeat ~ until

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; 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,[8] Erlang, S-Lang, Visual Prolog
// ActionScript, C (C99), C++, C#, D, Go, Object Pascal (Delphi), Java, JavaScript, PHP, Scala
' Visual Basic, VBScript, RealBasic
! Fortran, Basic Plus, Inform
; AutoHotkey, AutoIt, Lisp, Scheme, many assemblers
-- Euphoria, Haskell, SQL, Ada, AppleScript, Eiffel, Lua, VHDL
* COBOL, PAW, many assemblers
|| Curl
" Vimscript
\ Forth
:: Batch file[9]

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
/* */ ActionScript, AutoHotkey, C, C++, C#, CSS, D, Go, Java, JavaScript, PHP, PL/I, Scala (can be nested), SQL, Visual Prolog
/+ +/ D (can be nested)
/# #/ Cobra (can be nested)
<# #> Powershell
=begin =cut Perl
=begin =end Ruby
#<tag> #</tag> S-Lang
{- -} Haskell
(* *) Object Pascal (Delphi), ML, Mathematica, Pascal, Applescript, OCaml (can be nested), Maple
{ } Object Pascal (Delphi), Pascal
<!-- --> HTML, XML
|# #| Curl
%{ %} MATLAB[8]
#| |# Lisp
--[[ ]] Lua

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.

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.

Haskell

  • Haskell's comments can be stacked as brackets: {- some {-comments-} here -},

Esoteric languages

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, 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, 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++, 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)
HTML (see SGML below)
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 */
PILOT R:InlineComment
PL/SQL and TSQL -- InlineComment /* BlockComment */
REALbasic ' InlineComment
// InlineComment
rem InlineComment
SAS * BlockComment;
/* BlockComment */
Seed7 # InlineComment (* BlockComment *)
Simula comment BlockComment;
! BlockComment;
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 % InlineComment /* BlockComment */
XML, including XHTML <!--BlockComment--> (comment must not contain -- and must not start or end with single -)

See also

References

  1. ^ a b 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. ^ http://ss64.com/nt/syntax-brackets.html
  5. ^ Mathworks.com
  6. ^ Mathworks.com
  7. ^ For an M-file (MATLAB source) to be accessible by name, its parent directory must be in the search path (or current directory).
  8. ^ a b Mathworks.com
  9. ^ SS64.com

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