Parameterized macro
Encyclopedia
In computer science
, a parameterized macro is a type of 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
, this is a typical macro that is not a parameterized macro:
#define PI 3.14159
This causes the string "PI" to be replaced with "3.14159" wherever it occurs. It will always be replaced by this string, and the resulting string cannot be modified in any way. An example of a parameterized macro, on the other hand, is this:
#define pred(x) ((x)-1)
What this macro expands to depends on what argument x is passed to it. Here are some possible expansions:
pred(2) → ((2) -1)
pred(y+2) → ((y+2) -1)
pred(f(5)) → ((f(5))-1)
Parameterized macros are a useful source-level mechanism for performing in-line expansion
, but in languages such as C
where they use simple textual substitution, they have a number of severe disadvantages over other mechanisms for performing in-line expansion, such as inline function
s.
The parameterized macros used in languages such as Lisp
, PL/I
and Scheme, on the other hand, are much more powerful, able to make decisions about what code to produce based on their arguments; thus, they can effectively be used to perform run-time code generation.
Computer science
Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...
, a parameterized macro is a type of 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
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
, this is a typical macro that is not a parameterized macro:
#define PI 3.14159
This causes the string "PI" to be replaced with "3.14159" wherever it occurs. It will always be replaced by this string, and the resulting string cannot be modified in any way. An example of a parameterized macro, on the other hand, is this:
#define pred(x) ((x)-1)
What this macro expands to depends on what argument x is passed to it. Here are some possible expansions:
pred(2) → ((2) -1)
pred(y+2) → ((y+2) -1)
pred(f(5)) → ((f(5))-1)
Parameterized macros are a useful source-level mechanism for performing in-line expansion
Inline expansion
In computing, inline expansion, or inlining, is a manual or compiler optimization that replaces a function call site with the body of the callee. This optimization may improve time and space usage at runtime, at the possible cost of increasing the final size of the program In computing, inline...
, but in languages such as C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
where they use simple textual substitution, they have a number of severe disadvantages over other mechanisms for performing in-line expansion, such as inline function
Inline function
In various versions of the C and C++ programming languages, an inline function is a function upon which the compiler has been requested to perform inline expansion...
s.
The parameterized macros used in languages such as Lisp
Lisp programming language
Lisp is a family of computer programming languages with a long history and a distinctive, fully parenthesized syntax. Originally specified in 1958, Lisp is the second-oldest high-level programming language in widespread use today; only Fortran is older...
, PL/I
PL/I
PL/I is a procedural, imperative computer programming language designed for scientific, engineering, business and systems programming applications...
and Scheme, on the other hand, are much more powerful, able to make decisions about what code to produce based on their arguments; thus, they can effectively be used to perform run-time code generation.