• Open up and create a new Cocoa application in Project Builder.
• Go to Project -> Add Frameworks and add the MathLink framework to your project.
• In which ever file that will use MathLink, add this header: #include <mathlink/mathlink.h> Refer to MLController.m for an example.
• A sample Cocoa program is available, including the source code, Project Builder files, and interface nib. Download it at MLExample.tgz. Use either Untar, StuffIt Expander™, or the command tar -xvzf MLExample.tgz to uncompress the file.
• As always, to compile and run the project, click on the hammer-monitor icon to build and execute the program.
  

/* MLController.h */

#import <Cocoa/Cocoa.h>

@interface MLController : NSObject
{
    IBOutlet NSTextField *equationField;
    IBOutlet NSTextField *answerField;
}

- (IBAction) calculate : (id) sender;

@end 

/* MLController.m */          
#import "MLController.h"
#include <mathlink/mathlink.h>

@implementation MLController

- (IBAction) calculate : (id) sender
{
    float sum = 0;
    int argc = 4;
    char *argv[5] = {"-linkname",
                     " '/Applications/Mathematica 4.2.app/Contents/MacOS/MathKernel' -mathlink",
                     "-linkmode",
                     "launch",
                     NULL};
    MLINK lp;
    MLEnvironment env;
    char *expr;
        
    expr = [[equationField stringValue] cString];
    
    env = MLInitialize(NULL);
    
    if (env == NULL)
    {
        NSBeep();
        NSRunAlertPanel(@"Error", @"MathLink Environment could not be initialized.", @"OK", nil, nil);
        [NSApp terminate:self];
    }
    
    lp = MLOpen(argc, argv);
    
    if (lp == NULL)
    {
        NSBeep();
        NSRunAlertPanel(@"Error", @"MathLink could not be opened.", @"OK", nil, nil);
        [NSApp terminate:self];
    }

    MLPutFunction(lp, "EvaluatePacket", 1);
    MLPutFunction(lp, "ToExpression", 1);
    MLPutString(lp, expr);
    MLEndPacket(lp);

    while (MLNextPacket(lp) != RETURNPKT) MLNewPacket(lp);

    MLGetFloat(lp, &sum);

    MLClose(lp);
    MLDeinitialize(env);
                                                       
    [answerField setFloatValue: sum];
}

@end