Header

Extending EEL

Important notes about EEL Objects

Normally, you should NEVER INSTANTIATE class “body” structs, like EEL_vector, EEL_table, EEL_function, EEL_module or corresponding structs for user defined classes. Doing so WILL NOT RESULT IN VALID EEL OBJECTS.

Use EEL_ALLOC_OBJECT() to create proper EEL object with headers.
Use EEL_MAKE_CAST(MyType) to create an inline function MyType *o2MyType(EEL_object *o), that casts an EEL_object pointer to a pointer to MyType.

Adding a C function

Implement the function:

 static int my_cfunction(EEL_vm *vm)
 {
     EEL_value *arg = vm->heap + vm->argv;
     EEL_value *res = vm->heap + vm->resv;
     if(arg[0].type != EEL_TINTEGER)
         return EEL_XWRONGTYPE;
     if(arg[1].type != EEL_TINTEGER)
         return EEL_XWRONGTYPE;
     res->type = EEL_TINTEGER;
     res->integer.v = arg[0].integer.v + arg[1].integer.v;
 }

Register the function with the compiler:
```
 eel_register_cfunction(es, 1, "sum", 2, 0, 0, my_function);
```
Where the arguments are state, number of results, name in EEL, number of required arguments, number of optional arguments, number of tuple arguments and the address of the function.

Adding a class

Define a “body struct” to hold the private data of an instance:

 typedef struct
 {
     int	some_field;
     int	some_other_field;
 } MY_class;

Define a cast function to get at your struct inside an instance:
```
 EEL_MAKE_CAST(MY_class)
```

Implement a constructor:

 static EEL_exceptions mc_construct(EEL_vm *vm, EEL_object *eo,
         EEL_value *op1, EEL_value *op2)
 {
     MY_class *mc;
     eo = EEL_ALLOC_OBJECT(vm, MY_class);
     if(!eo)
         return EEL_XMEMORY;
     mc = o2MY_class(eo);
     mc->some_field = ...;
     ...
     op1->type = EEL_TOBJECT;
     op1->object.v = eo;
     return 0;
 }

Implement a destructor:

 static EEL_exceptions mc_destruct(EEL_vm *vm, EEL_object *eo,
         EEL_value *op1, EEL_value *op2)
 {
     eel_free(vm, eo);
     return 0;
 }

 int my_class_cid = eel_add_class(es, "myclass", mc_create, mc_destroy);

Implement some metamethods (one in our example):

 static EEL_exceptions mc_setindex(EEL_vm *vm, EEL_object *eo,
         EEL_value *op1, EEL_value *op2)
 {
     MY_class *mc = o2MY_class(eo);
     if(op1->type != EEL_TINTEGER)
         return EEL_XWRONGTYPE;
     if(op2->type != EEL_TINTEGER)
         return EEL_XWRONGTYPE;
     switch(op2->integer.v)
     {
       case 0:
         mc->some_field = op1->integer.v;
         break;
       case 1:
         mc->some_other_field = op1->integer.v;
         break;
       default:
         return EEL_XWRONGINDEX;
     }
     op1->type = EEL_TINTEGER;
     return 0;
 }

 eel_set_metamethod(es, my_class_cid, EEL_MM_SETINDEX, mc_setindex);