Perbandingan -- programming languages (syntax)

This is a comparison of programming language syntax.

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

• Forth 2 3 + 4 5 ** *

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.

Line continuation

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

• C and C++ preprocessor
• Falcon
• Mathematica
• Python
• Ruby

Backtick as last character of line

• Windows PowerShell

Hyphen as last character of line

• SQL*Plus

Left parenthesis as last character of line

• COMMAND.COM, cmd.exe: starting a parenthetical block can allow line continuation.^[4]

Underscore as last character of line

• Autoit
• Cobra
• Visual Basic

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

• 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>
• 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

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) { ... }:

• 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 ( ... )

• OCaml, Standard ML

Brackets [ ... ]

• Smalltalk (blocks are first class objects. aka 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)

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

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

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 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

• 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.

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