String Processing

Abstract

This chapter describes the principal techniques of string processing in Prolog, based on converting from atoms to lists and vice versa. The techniques are illustrated with examples of user-defined predicates to meet common string processing requirements.

After reading this chapter you should be able to:

• Use a built-in predicate to convert strings of characters to lists and vice versa

• Define predicates for the most common types of string processing

Practical Exercise 10

• (1) Define and test a predicate spalindrome to check whether a string is a palindrome, e.g.

• ?- spalindrome(’abcd dcba’).

• yes

• ?- spalindrome(’xyz’).

• no

• (2) Use the name predicate to define and test a predicate remove_final that removes any final spaces from a string, e.g.

• ?- remove_final(’hello world ’,X).

• X = ’hello world’

• ?- remove_final(’hello world’,X).

• X = ’hello world’

• (3) Define and test a predicate replace to replace the first character in a string by the character ? (which has ASCII value 63), e.g.

• ?- replace(’abcde’,X).

• X = ’?bcde’