The square brackets [ and ] have a special function within a macro definition. The preprocessor first attempts to expand a macro definition when it is stored in the macro table, and then again when it is subsequently invoked. Each level of square brackets protects the macro definition from one level of expansion. One pair of square brackets means that a macro definition is not expanded when stored in the macro table, but is expanded when invoked. Two levels of square brackets prevents macro expansion from taking place at all. For example, if the definitions are in the order

		macro:(nb:,10)
		macro:(maxb:,arith:(5,*,nb:))

the definition of maxb: is stored in the RFPP macro table as 50.

Alternatively, if the order of macros is

		macro:(maxb:,[arith:(5,*,nb:)])
		macro:(nb:,10)

the definition of maxb: is stored as the string ARITH:(5,*,NB:) in the macro table. It will be output into the Fortran code as 50.

In another example, the macro definition

		macro:(defn:,[[maxmax:]])

would be stored in the macro table as [MAXMAX:] and when invoked it would be output in the Fortran as MAXMAX:. In this case the string maxmax: is not treated as a macro.

This sequence of definitions will be processed as follows.

		macro:(firstname:,bill)
		macro:(fullname:,firstname:$B lastname:)
		macro:(lastname:,jones)

The macro firstname: will be stored in the macro table as BILL. The macro fullname:will be stored as BILL lastname: since lastname: is not yet defined. The macro lastname: will be stored as JONES. When the macro fullname: appears in the ratmac code, the definition string is scanned again and the macro definition of lastname: is inserted. The string BILL JONES is inserted into the Fortran code.

For this sequence, the use of square brackets is essential.

		macro:(nbyte:,4)
		macro:(length:,arith:(nword:,*,nbyte:))
		macro:(nword:,100)

This set of definitions will cause incorrect Fortran code to be generated because RFPP will attempt to expand the definition of length: before the definition of nword: is available. The correct definition of length: is

		macro:(length:,[arith:(nword:,*,nbyte:)])

because the square brackets prevent macro expansion until the invocation of length:.