Macro Substitution

In computer programming, a macro (short for "macro instruction"; ) is a rule or pattern that specifies how a certain input should be mapped to a replacement output. Applying a macro to an input is known as macro expansion. The input and output may be a sequence of lexical tokens or characters, or a syntax tree. Character macros are supported in software applications to make it easy to invoke common command sequences. Token and tree macros are supported in some programming languages to enable code reuse or to extend the language, sometimes for domain-specific languages.

Macros are used to make a sequence of computing instructions available to the programmer as a single program statement, making the programming task less tedious and less error-prone. (Thus, they are called "macros" because a "big" block of code can be expanded from a "small" sequence of characters.) Macros often allow positional or keyword parameters that dictate what the conditional assembler program generates and have been used to create entire programs or program suites according to such variables as operating system, platform or other factors. The term derives from "macro instruction", and such expansions were originally used in generating assembly language code.

Keyboard and mouse macros

Keyboard macros and mouse macros allow short sequences of keystrokes and mouse actions to transform into other, usually more time-consuming, sequences of keystrokes and mouse actions. In this way, frequently used or repetitive sequences of keystrokes and mouse movements can be automated. Separate programs for creating these macros are called macro recorders.

During the 1980s, macro programs – originally SmartKey, then SuperKey, KeyWorks, Prokey – were very popular, first as a means to automatically format screenplays, then for a variety of user input tasks. These programs were based on the TSR (terminate and stay resident) mode of operation and applied to all keyboard input, no matter in which context it occurred. They have to some extent fallen into obsolescence following the advent of mouse-driven user interfaces and the availability of keyboard and mouse macros in applications such as word processors and spreadsheets, making it possible to create application-sensitive keyboard macros.

Keyboard macros can be used in massively multiplayer online role-playing games (MMORPGs) to perform repetitive, but lucrative tasks, thus accumulating resources. As this is done without human effort, it can skew the economy of the game. For this reason, use of macros is a violation of the TOS or EULA of most MMORPGs, and their administrators spend considerable effort to suppress them.

Application macros and scripting

Keyboard and mouse macros that are created using an application's built-in macro features are sometimes called application macros. They are created by carrying out the sequence once and letting the application record the actions. An underlying macro programming language, most commonly a scripting language, with direct access to the features of the application may also exist.

The programmers' text editor, Emacs, (short for "editing macros") follows this idea to a conclusion. In effect, most of the editor is made of macros. Emacs was originally devised as a set of macros in the editing language TECO; it was later ported to dialects of Lisp.

Another programmers' text editor, Vim (a descendant of vi), also has an implementation of keyboard macros. It can record into a register (macro) what a person types on the keyboard and it can be replayed or edited just like VBA macros for Microsoft Office. Vim also has a scripting language called Vimscript to create macros.

Visual Basic for Applications (VBA) is a programming language included in Microsoft Office from Office 97 through Office 2019 (although it was available in some components of Office prior to Office 97). However, its function has evolved from and replaced the macro languages that were originally included in some of these applications.

XEDIT, running on the Conversational Monitor System (CMS) component of VM, supports macros written in EXEC, EXEC2 and REXX, and some CMS commands were actually wrappers around XEDIT macros. The Hessling Editor (THE), a partial clone of XEDIT, supports Rexx macros using Regina and Open Object REXX (oorexx). Many common applications, and some on PCs, use Rexx as a scripting language.

Macro virus

VBA has access to most Microsoft Windows system calls and executes when documents are opened. This makes it relatively easy to write computer viruses in VBA, commonly known as macro viruses. In the mid-to-late 1990s, this became one of the most common types of computer virus. However, during the late 1990s and to date, Microsoft has been patching and updating its programs. In addition, current anti-virus programs immediately counteract such attacks.

Parameterized macro

A parameterized macro is a macro that is able to insert given objects into its expansion. This gives the macro some of the power of a function.

As a simple example, in the C programming language