Understanding the Power of CLIPS: A Step-by-Step Guide to Integrating Prolog Reasoning in iPhone Apps

Understanding CLIPS (.clp) Files and Integrating Them into iPhone Applications

Introduction to CLIPS

CLIPS (Common Lisp Interface to Prolog Systems) is a Common Lisp-based programming language that allows developers to integrate Prolog reasoning capabilities into their applications. It provides a way to access and manipulate knowledge bases, perform inference, and execute logic programs written in Common Lisp.

In this article, we will explore the process of loading and executing .clp files within an iPhone application using CLIPS. We will delve into the intricacies of CLIPS, discuss common pitfalls, and provide practical examples to help you get started with integrating CLIPS into your iOS projects.

Loading CLIPS Files

To load a .clp file in your iPhone application, you need to follow these steps:

Create an instance of InitializeEnvironment() to initialize the CLIPS environment.
Use Load() to load the .clp file into the CLIPS environment.
Execute the loaded code using Run(-1).
Increment and decrement GCLocks() to ensure proper synchronization.

- (void)viewDidLoad {
    [super viewDidLoad];
    
    InitializeEnvironment();
    Clear();

    NSString *filePath = [[NSBundle mainBundle]
                          pathForResource:@"autodemo" ofType:@"clp"];
    char *clipsFileChar = (char *)[filePath cStringUsingEncoding:NSASCIIStringEncoding];

    IncrementGCLocks();
    Load(clipsFileChar);
    Reset();
    Run(-1);

    DecrementGCLocks();

    [self nextUIState];
}

Executing Loaded Code

To execute the loaded code, you need to use the EnvEval() function. This function takes a string representing the Prolog query and returns the result as a DATA_OBJECT.

- (void)nextUIState {
    DATA_OBJECT theDO;
    NSString * evalS = @"(find-all-facts ((?f state-list)) TRUE)";
    char *evalStr = (char *)[evalS cStringUsingEncoding:NSASCIIStringEncoding];

    int j = EnvEval(GetCurrentEnvironment(), evalStr, &theDO);
    NSLog(@"j = %d",j);

    if(factDict)
    {
        [factDict release];
        factDict = nil;

        factDict = [[NSMutableDictionary alloc] init];
    }

    id value = [self objectForDataObject:&theDO];

    NSLog(@"%@",[value description]);    
}

Object for Data Object

The objectForDataObject method is used to convert the DATA_OBJECT returned by EnvEval() into a usable form.

- (id) objectForDataObject: (DATA_OBJECT*) arg {
    switch(arg->type)
    {
        case FACT_ADDRESS:
        {

            DATA_OBJECT data = { 0 };
            struct fact* aFact = (struct fact*) arg->value;

            if(EnvGetFactSlot(GetCurrentEnvironment(),aFact,(char*)[@"current" UTF8String],&data))
            {
                [factDict setObject:[self objectForDataObject: &data] forKey:@"current"];
                [factDict retain];
            }
            return factDict;
        }
        case SYMBOL:
        {
            NSString *str = [NSString stringWithUTF8String: ValueToString(arg->value)];
            if ([str isEqual: @"nil"]) return nil;
            if ([str hasPrefix: @"&lt;&lt;&lt;"] &amp;&amp; [str hasSuffix: @"&gt;&gt;&gt;"])
            {
                return [self dataFromSymbolString: str];
            }
            return str;
        }
        case STRING:
        {
            return [NSString stringWithUTF8String: ValueToString(arg->value)]; 
        }
        case INTEGER:
        {
            return [NSNumber numberWithInt: ValueToInteger(arg->value)];
        }
        case FLOAT:
        {
            return [NSNumber numberWithDouble: ValueToDouble(arg->value)];
        }
        case EXTERNAL_ADDRESS:
        {
            return (id) arg->value;
        }
        case MULTIFIELD:
        {
            int i, count = GetpDOLength(arg);
            NSMutableArray *args = [NSMutableArray arrayWithCapacity: count];
            FIELD_PTR fptr = (FIELD_PTR) GetMFPtr(GetpValue(arg),GetpDOBegin(arg));
            for(i = 0; i < count; ++i, ++fptr)
            {
                DATA_OBJECT dobj;
                dobj.type = fptr->type;
                dobj.value = fptr->value;
                [args addObject: [self objectForDataObject: &dobj]];
            }
            return args;
        }
        default:
            return nil;
    }
}

Conclusion

Integrating CLIPS into an iPhone application can be a powerful way to add Prolog reasoning capabilities. By following the steps outlined in this article, you can load and execute .clp files within your iOS project.

However, keep in mind that CLIPS is a complex system with many nuances. Make sure to consult the official documentation and seek guidance from experienced developers if you encounter any difficulties.

Remember to always increment and decrement GCLocks() to ensure proper synchronization, and use Load() to load .clp files into the CLIPS environment.

With this knowledge, you are well-equipped to tackle complex reasoning tasks within your iOS applications.

Last modified on 2023-08-25