Question

How do I go about evaluating logical expression like “VERB1 OR (VERB2 AND VERB3) OR (VERB4)” entered at runtime. VERB* are placeholder to evaluate certain conditions. For example, VERB1 might mean check for the existence of a record in database.

In expression “VERB1 OR (VERB2 AND VERB3) OR (VERB4)”, other verbs should not be executed if VERB1 is true

EDIT: Example described at http://www.alittlemadness.com/2006/06/05/antlr-by-example-part-1-the-language/ seems very similar to what I am trying to do. However, the optimization step (other verbs should not be executed if VERB1 is true) doesn’t seem to be there.

Answer 1

If you can use || and && in place of AND and OR, you can just use groovy’s missing property methods and the GroovyShell base class setting like so:

import org.codehaus.groovy.control.CompilerConfiguration

// The command to be executes
def command = "VERB1 || (VERB2 && VERB3) || (VERB4)"

// Set a base class for the GroovyShell
new CompilerConfiguration().with { compiler ->
  compiler.scriptBaseClass = 'VerbHandlingBaseClass'
  new GroovyShell( this.class.classLoader, new Binding(), compiler ).with { shell ->
    // and evaluate the command
    shell.evaluate( command )
  }
}

abstract class VerbHandlingBaseClass extends Script {
  boolean VERB1() {
    System.out.println( 'CHECK THE DATABASE, RETURN FALSE' )
    false
  }

  boolean VERB2() {
    System.out.println( 'WRITE A LOG ENTRY RETURN TRUE' )
    true
  }

  boolean VERB3() {
    System.out.println( 'VALIDATE SOMETHING, RETURN TRUE' )
    true
  }

  boolean VERB4() {
    System.out.println( 'THIS WONT BE REACHED, AS VERB2 && VERB3 == true' )
    true
  }

  def propertyMissing( String name ) {
    "$name"()
  }
}

That should print:

CHECK THE DATABASE, RETURN FALSE
WRITE A LOG ENTRY RETURN TRUE
VALIDATE SOMETHING, RETURN TRUE