Question: Implement recursive method

I have programmed a bisection procedure below, and i was just wondering how i would change this into a recursive version of the method. I don't really understand what is ment by recursive?

bisection:=proc(f,X,Y,Z)
local a,b,c,d;
a:=X:
b:=Y:
d:=Z:
while(abs(b-a)>d) do
c:=(a+b)/2:
if sign(f(c))=sign(f(a)) then a:=c else b:=c
fi:
od:
print(evalf((a+b)/2)):
end proc:

Many thanks!!!

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