What kind of a structure can the cddaar procedure be applied
to? What must its operand look like?
The operand must be a pair (pr1) in which the first component
is also a pair (pr2); moreover, the first component of
pr2 must also be a pair (pr3), and the second
component of pr3 must also be a pair
(pr4).
Which of the elements of such a structure does cddaar
return?
It returns the second component of pr4.
> (define example-1 (cons (cons (cons #f (cons #f #t)) #f) #f))
> (cddaar example-1)
#t
> (define example-2 (cons (cons (cons (cons 1 2) (cons 3 4))
(cons (cons 5 6) (cons 7 8)))
(cons (cons (cons 9 10) (cons 11 12))
(cons (cons 13 14) (cons 15 16)))))
> (cddaar example-2)
4
What happens if the structure has the wrong shape? It is an error, so under most implementations the program crashes:
> (cddaar (cons (cons (cons 1 2) (cons 3 4))
(cons (cons 5 6) (cons 7 8))))
ERROR: cddaar: Wrong type in arg1 2
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