ifelse: provides conditional selection of code. This macro contains a rudimentary form of logical branching which may be used to select alternate arguments in the macro definition.

	ifelse:(arg1, arg2, arg3, arg4)

argN represents a literal string of characters not containing a comma, parenthesis or square bracket.

If arg1 is identical to arg2, then output arg3 else output arg4

	N=ifelse:(ftntype:,77,NBYTE,NINTR)

tests the defined value of ftntype: and outputs N=NBYTE if it is defined as '77' or N=NINTR if it is defined as '66'.