How would you reduce macros with parameters?

• You already know how to do it.

  Let f( x ) = x * (x + 1) / 2 in f( f( 3 ) )

• The general rule is:

  a function f, with formal parameter x, applied to an actual parameter y

  reduces to

  the body of the function f, with the actual parameter x substituted for the formal parameter y.