Sajun.org
:'''''Macro''' (meaning "large" or "wide") is also applied to
macroeconomics, and
macroscopic or "macro"
lenses.''
:'''''Macro''' (meaning a kind of close-up photography) is found at
Macro photography.''
A '''macro''' is an
abstraction, whereby a certain textual
pattern is replaced according to a defined set of rules. The
interpreter or
compiler automatically replaces the pattern when it is encountered. In compiled languages, ''macro-expansion'' always happens at compile-time.
The purpose of macros is to either
automate frequently-used
sequences or enable a more powerful abstraction -- but these are often the same thing.
Languages such as
C and
assembly language have simple macro systems, implemented as preprocessors to the compiler or assembler. C preprocessor macros work by simple textual search-and-replace. More elaborate macros are available to C programmers by using an additional text-processing language such as
M4.
Lisp languages such as
Common Lisp and
Scheme have more elaborate macro systems: In Lisp, macros behave like functions transforming program text, with the full language available to express such transformations.
Whereas a C macro may define a simple replacement of one piece of syntax with another, a Lisp macro can control the evaluation of sections of code, creating new syntactic constructs indistinguishable from those built into the language. For instance, in a Lisp dialect that has
cond but lacks
if, it is possible to define the latter in terms of the former using macros. Entire major extensions to Lisp syntax, such as the
CLOS system for
object-oriented programming, have been defined as macros.
==Keyboard macros==
'''Keyboard macros''' and editor macros are used interactively on a
graphical user interface and
text editor, respectively. These allow short sequences of keystrokes substitute for long sequences of commands, and can provide a simple form of
automation for
repetitive tasks.
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.
==Macro languages==
A '''macro language''' is a programming language in which all or most computation is done by expanding macros. Macro languages are not widely used for general-purpose programming, but are common in text processing applications. Examples include M4 (mentioned previously) and
TeX.
==Microsoft Word and macro viruses==
Visual Basic for Applications, the macro programming language in
Microsoft Office, has access to many operating system functions and supports automatic execution of macros when a document is opened. This makes it possible to write
computer viruses in this language. In the mid-to-late
1990s, so-called '''
macro viruses''' became one of the most common types of computer virus. Other projects with macro languages, such as
OpenOffice.org, have deliberately excluded certain functionality (''e.g.'' automatic execution) from their macro language so as to avoid susceptibility to this problem.
de:Makro fr:macro-dfinition
