Regular Expressions in CLIPS

Our first program will demonstrate the use of regular expressions in Java. Here’s the full source code with examples of common regex-related tasks.

import java.util.regex.*;
import java.util.Arrays;

public class RegularExpressions {
    public static void main(String[] args) {
        // This tests whether a pattern matches a string.
        boolean match = Pattern.matches("p([a-z]+)ch", "peach");
        System.out.println(match);

        // For other regex tasks, you'll need to compile a Pattern object.
        Pattern r = Pattern.compile("p([a-z]+)ch");

        // Many methods are available on these objects. Here's a match test like we saw earlier.
        Matcher m = r.matcher("peach");
        System.out.println(m.matches());

        // This finds the match for the regex.
        m = r.matcher("peach punch");
        m.find();
        System.out.println(m.group());

        // This also finds the first match but returns the start and end indexes for the match.
        m = r.matcher("peach punch");
        m.find();
        System.out.println("idx: [" + m.start() + " " + m.end() + "]");

        // The group methods include information about both the whole-pattern matches 
        // and the submatches within those matches.
        m = r.matcher("peach punch");
        m.find();
        System.out.println(Arrays.toString(new String[]{m.group(), m.group(1)}));

        // To find all matches in the input, we can use a while loop with find().
        m = r.matcher("peach punch pinch");
        while (m.find()) {
            System.out.print(m.group() + " ");
        }
        System.out.println();

        // The replaceAll method can be used to replace subsets of strings with other values.
        String result = r.matcher("a peach").replaceAll("<fruit>");
        System.out.println(result);

        // The replaceAll method also allows you to transform matched text with a given function.
        result = r.matcher("a peach").replaceAll(match -> match.group().toUpperCase());
        System.out.println(result);
    }
}

To run the program, compile it and use java:

$ javac RegularExpressions.java
$ java RegularExpressions
true
true
peach
idx: [0 5]
[peach, ea]
peach punch pinch 
a <fruit>
a PEACH

Java’s regular expression support is provided by the java.util.regex package. The Pattern class is used to compile regex patterns, and the Matcher class is used to perform match operations on a character sequence.

Some key differences from the Go version:

Java uses Pattern.matches() for simple matching, which is equivalent to Go’s regexp.MatchString().
In Java, you need to create a Matcher object to perform operations like finding matches or replacing text.
Java’s find() method is similar to Go’s FindString(), but you need to call group() to get the matched text.
Java doesn’t have direct equivalents for some of Go’s methods like FindStringSubmatchIndex(). You need to use a combination of find(), start(), and end() methods to achieve similar functionality.
For replacement operations, Java uses replaceAll() method, which can take either a string or a function (via lambda expression in Java 8+) for replacement.

For a complete reference on Java regular expressions, check the official Java documentation for the java.util.regex package.

Text Templates in CLIPS

Json in CLIPS

Learn X By Example

Title here

Regular Expressions in CLIPS