User defined function

Hi,
   I have written a small Makefile but it is not working as per my
expectations, can someone please point out what is wrong with it:

define check_defined
    @$(1)=1;
endefall:
    $(call check_defined, hello)
ifeq ($(hello),1)
    sleep 10
endif

I am expecting, when I invoke "make all" it should sleep for 10 secs but it
is not happening, what is wrong with it and how can I achieve it?

Thanks,
-Rajeev