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

When a programming languages has statements, they typically have conventions for:

• statement separators;
• statement terminators; and
• line continuation

A statement separator demarcates the boundary between two separate statements. A statement terminator defines the end of an individual statement. Languages that interpret the end of line to be the end of a statement are called "line-oriented" languages.

"Line continuation" is a convention in line-oriented 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

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
• JavaScript – Lines terminate with semicolon (which may be inferred)
• Lua
• OCaml

Ampersand as last character of line

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

Backslash as last character of line

• bash^[5] and other Unix shells
• C, C++ preprocessor
• Mathematica, Wolfram Language
• Python^[6]
• Ruby
• JavaScript – only within single- or double-quoted strings

Backtick as last character of line

• 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.^[7] (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^[8]
• Ruby: left parenthesis, left square bracket, or left curly bracket

Operator as last object of line

• Ruby (comment may follow operator)

Operator as first character of continued line

• AutoHotkey: Any expression operators except ++ and --, and a comma or a period^[9]

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 prior 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 prior command.

[End and Begin] using normal quotes

• C, 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

• addpath(directory)MATLAB^[10]
• COPY filename. COBOL
• :-include("filename"). Prolog
• #include file="filename" ASP
• #include "filename", AutoHotkey, AutoIt, C, C++
• #include <filename>AutoHotkey, AutoIt, C, C++
• #import "filename", Objective-C
• #import <filename> Objective-C
• Import["filename"] Mathematica, Wolfram Language
• include 'filename' Fortran
• include "filename";PHP
• include [filename] program, Pick Basic
• #include [filename] program Pick Basic
• include!("filename");Rust
• load "filename"Ruby
• load %filename Red
• require('filename') Lua
• require "filename"; Perl, PHP
• require "filename" Ruby
• source(""filename"") R
• @import("filename");Zig

Package import

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

Class import

• from module import Class Python
• import package.class Java, MATLAB, kotlin
• import class from "modname";, JavaScript
• import {class} from "modname";, JavaScript
• import {class as altname} from "modname";JavaScript
• import package.class, Scala
• import package.{ class1 => alternativeName, class2 }, Scala
• import package._Scala
• use Namespace\ClassName;, PHP
• use Namespace\ClassName as AliasName; PHP

Procedure/function import

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

Constant import

• use const Namespace\CONST_NAME; PHP

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

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

Required to access code

• import altname "package/name" Go
• import altname from "modname";JavaScript
• import modulePython

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, V (Vlang), C#, D, Perl, PHP (for & loop loops, or pass a block as argument), R, Rust, Scala, S-Lang, Swift, PowerShell, Haskell (in do-notation), AutoHotkey, Zig

Parentheses ( ... )

• Batchfile, F# (lightweight syntax),^[11] OCaml, Prolog, Standard ML

Square brackets [ ... ]

• Rebol, Red, Self, Smalltalk (blocks are first class objects. a.k.a. closures)

begin ... end

• Ada, ALGOL, F# (verbose syntax),^[11] Pascal, Ruby (for, do/while & do/until loops), OCaml, SCL, Simula, Erlang.

do ... end

• PL/I, REXX

do ... done

• Bash (for & while loops), F# (verbose syntax)^[11] 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):

• 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: Boo, Cobra, CoffeeScript, F#, Haskell (in do-notation when braces are omitted), LiveScript, occam, Python, Nemerle (Optional; the user may use white-space sensitive syntax instead of the curly-brace syntax if they so desire), Nim, Scala (Optional, as in Nemerle)
• Free-form languages: most descendants from ALGOL (including C, Pascal, and Perl); Lisp languages

Others

• Ada, Visual Basic, Seed7: if ... end if
• APL: :If ... :EndIf or :If ... :End
• 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.
• Visual Basic .Net: If ... End If, For ... Next, Do ... Loop
• Small Basic: If ... EndIf, For ... EndFor, While ... EndWhile

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. In the examples, the symbol ~ represents the comment; and, the symbols surrounding it are understood by the interpreters/compilers as the delimiters.

Examples:

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 prior 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-quotes to comment-out lines of source, does not actually form a comment.^[21] The enclosed text becomes a string literal, which Python usually ignores (except when it is the first statement in the body of a module, class or function; see docstring).

Elixir

• The above trick used in Python also works in Elixir, but the compiler will throw a warning if it spots this. To surpress the warning, one would need to prepend the sigil ~S (which prevents string interpolation) to the triple-quoted string, leading to the final construct ~S""" ... """. In addition, Elixir supports a limited form of block comments as an official language feature, but as in Perl, this construct is entirely intended to write documentation. Unlike in Perl, it cannot be used as a workaround, being limited to certain parts of the code and throwing errors or even surpressing functions if used elsewhere.^[22]

Raku

• Raku uses #`(...) to denote block comments.^[23] Raku 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).

Ruby

• Block comment in Ruby opens at =begin line and closes at =end line.

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 comment 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.