Switch Define the macro switch, which takes in an expression expr and a list of pairs, cases, where the first element of the pair is some value and the second element is a single expression. switch will evaluate the expression contained in the list of cases that corresponds to the value that expr evaluates to. scm> (switch ( 1 1) ((1 (print 'a)) (2 (print 'b)) (3 (print 'c b You may assume that the value expr evaluates to is always the first element of one of the pairs in cases. You can also assume that the first value of each pair in cases is a value. (define-macro (switch expr cases) (cons (map ( () (cons (cdr case))) cases)) )