SICP exercise 2.33

Problem

Fill in the missing expressions to complete the following definitions of some basic list-manipulation operations as accumulations:

Here's the definition of accumulate as given in the text:

Here's an implementation of map which uses accumulate:

Test:

Output:

(4 9 25 49 64)

An implementation of append:

Test:

Output:

(1 2 3 4 5 6 7 8)

And finally, length:

Test:

Output: