How to make an Objective-C project work on Ubuntu?

My files are:

Fraction.h

    #import <Foundation/NSObject.h>

    @interface Fraction: NSObject {
        int numerator;
        int denominator;
    }

    -(void) print;
    -(void) setNumerator: (int) n;
    -(void) setDenominator: (int) d;
    -(int) numerator;
    -(int) denominator;
    @end

Fraction.m

    #import "Fraction.h"
    #import <stdio.h>

    @implementation Fraction
    -(void) print {
        printf( "%i/%i", numerator, denominator );
    }

    -(void) setNumerator: (int) n {
        numerator = n;
    }

    -(void) setDenominator: (int) d {
        denominator = d;
    }

    -(int) denominator {
        return denominator;
    }

    -(int) numerator {
        return numerator;
    }
    @end

main.m

    #import <stdio.h>
    #import "Fraction.h"

    int main( int argc, const char *argv[] ) {
        // create a new instance
        Fraction *frac = [[Fraction alloc] init];

        // set the values
        [frac setNumerator: 1];
        [frac setDenominator: 3];

        // print it
        printf( "The fraction is: " );
        [frac print];
        printf( "\n" );

        // free memory
        [frac release];

        return 0;
    }

I've tried two approaches to compile it:

1. Pure gcc:

   $ sudo apt-get install gobjc gnustep gnustep-devel
   $ gcc `gnustep-config --objc-flags` -o main main.m -lobjc -lgnustep-base
   /tmp/ccIQKhfH.o:(.data.rel+0x0): undefined reference to `__objc_class_name_Fraction'
   

2. I created a GNUmakefile Makefile:

   include ${GNUSTEP_MAKEFILES}/common.make
   
   
   TOOL_NAME = main
   main_OBJC_FILES = main.m
   
   
   include ${GNUSTEP_MAKEFILES}/tool.make
   

   ... and ran:

   $ source /usr/share/GNUstep/Makefiles/GNUstep.sh
   $ make
   Making all for tool main...
    Linking tool main ...
   ./obj/main.o:(.data.rel+0x0): undefined reference to `__objc_class_name_Fraction'
   

So in both cases compiler gets stuck at

    undefined reference to `__objc_class_name_Fraction'

Do you have and idea how to resolve this issue?