PPT Slide

The Keyword &optional means all following parameters are optional.

( defun mplus ( x y &optional ( m 1 ) )

( * m ( + x y ) ) )

( mplus 2 3 ) 5

( mplus 2 3 6 ) 30

ARBITRARY NUMBERS OF ARGUMENTS

The Keyword &rest says the parameter following it will name a list that an arbitrary number of corresponding arguments will be put into.

( defun mp2 ( v &rest vals )

( mapcar # '( lambda (x) (+ v x ) ) vals) )

( mp2 6 9 0 1 3 ) returns ( 15 6 7 9 )