| Coral 66 Language Reference Manual: For mission-critical applications | ||
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A Coral 66 compiler embodies a macro processor, which may be regarded as a self-contained routine which processes the text of the Coral program before passing it on to the compiler proper. Its function is to enable the programmer to define and to use convenient macro names, in the form of identifiers, to stand in place of cumbersome or obscure portions of text, typically code statements. Once a macro name has been defined, the processor expands it in accordance with the definition wherever it is subsequently used, until the definition is altered of canceled (. However the macro processor treats comments and character strings (see ) as indivisible entities, and does not expand any identifiers within these entities. No character which could form part of an identifier may be written adjacent to the use of a macro name or formal parameter, as this would inhibit the recognition of such names. A macro definition may be written into the source program wherever a declaration or statement could legally appear, and is removed from it by action of the macro processor.
In the simplest use, a macro name stands for a definite string of characters, the macro body. For example, the (fictitious) code statement
might be given the name "shift6". The macro definition would be written
The expansion, or body, can be any sequence of characters in which the string quotes are matched (but see ). Care must be taken to include brackets, such as BEGIN and END, as part of the macro body wherever there is the possibility that the context of the expansion may demand them.
A macro may have parameters as in the following example,
Subsequent occurrences of shift(6) would be expanded to the code statement in . A formal parameter, such as n above, must be written as an identifier. An actual parameter (e.g. 6) is any string of characters in which string quotes are matched, all round and square brackets are nested and matched, and all occurrences of a comma lie between round or square brackets. This rule enables commas to be used for separating actual parameters. The number of actual parameters must be the same as the number of formals, which are also separated by commas.
A macro definition may embody definitions or uses of other macros to any depth. When a macro is defined, the body is kept but not expanded. When the macro is used, it is as though the body were substituted into the program text, and it is during this substitution that any other macros encountered are processed. The use of a macro with parameters may be regarded as introducing virtual macros definitions for the formal parameters before the macro body is substituted. Thus, to continue the example from , the occurrence of shift(6) is equivalent to
followed immediately by deletion of the virtual macro n. Throughout
the scope of the macro shift, the formal parameter n may
not be defined as a macro name. A formal parameter may not be used in any
inner nested macro definition, neither in its body nor as a macro name nor
as a formal parameter. Furthermore, no identifier in an actual parameter
string, or its subsequent expansions, may be the same as any formal
parameter of the calling macro.
Macro definitions are valid from the point of definition until either the end of the program text is reached of the macro name is redefined or deleted. The scope of a macro is independent of the blocks structure of the program. To delete a macro the command
is used wherever a declaration or statement could appear. Alternatively, a macro name can be redefined. Macro definitions which have the same name are stacked, so that the most recent is the one which applies when the name is used. If a redefined macro is deleted, it is the most recent definition which is deleted, and the previous one is reinstated. 'Recent' and 'previous' refer to the sequence as processed by the macro processor.
Commentsentence ::=
COMMENT
any sequence of characters not including a semi-colon
;
Bracketedcomment ::=
(
any sequence of characters in which round brackets are matched
)
Endcomment ::=
Id
Macrodefinition ::=
DEFINE
Macroname " Macrobody " ;
DEFINE
Macroname ( Idlist ) " Macrobody " ;
Macroname ::=
Id
Macrobody ::=
any sequence of characters in which string quotes are matched
Macrodeletion ::=
DELETE
Macroname ;
Macrocall ::=
Macroname
Macroname ( Macrostringlist )
Macrostringlist ::=
Macrostring , Macrostringlist
Macrostring
Macrostring ::=
any sequence of characters in which commas are
protected by round or square brackets and in
which such brackets are properly matched and
nested