Macro (macro-instruction) Definition/Meaning:
Short for macro-instruction. An instruction in a programming
language (almost always but not necessarily assembly language) that is replaced by a
sequence of instructions prior to assembly or compiling. A macro-assembler
permits the user to define macros, specifying the macro-instruction form, its
arguments, and a replacement text (otherwise called the body of the macro), and
then allows macro-instructions to be interspersed among the assembly code. On
encountering a macro-instruction the assembler replaces it by the macro body,
substituting the parameters provided in the places marked in the macro body. The
macro thus provides a mechanism for inserting a particular body of text at
various places in a program (and is thus the same thing as an open subroutine,
though this nomenclature is obsolete).
A macro-processor provides similar facilities, though not in combination with an
assembler. It accepts macro definitions and then reads arbitrary text in which
macro calls (i.e. instances of a macro name) can occur. Text is copied to the
output until a macro name is encountered: when this happens the arguments
(parameters) are found and the macro call is replaced by the macro body in the
output stream, with appropriate substitution of the parameters.
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