Exercises on Section 4

For each of the following functions, give the signature and suggest a suitable precondition.

• (a) TOUPPER, which changes a string, containing only lower-case letters, into the corresponding string consisting of upper-case letters. (So, for example, TOUPPER(“word”) = “WORD”.)

• (b) REMOVELAST, which, given a sequence, deletes its last member.

• (c) LAST, which returns the last member of a sequence.

Suppose that the days of the week are represented by numbers, with Mon-day represented by 1, Tuesday represented by 2, and so on, with Sunday represented by 7. Describe a function TOMORROW2, giving the next day with Days represented in this way.

• (a) With s = “abcd”, evaluate each of:

  • (i) AT(1, s);

  • (ii) PUT(2, s, AT(1, s)).

• (b) For a general sequence s, describe how the sequence PUT(2, s, AT(1, s)) is obtained from s.

The functions AT and PUT were described in Activity 16.