Overloading Macro on Number of Arguments

I have two macros FOO2 and FOO3: #define FOO2(x,y) ... #define FOO3(x,y,z) ... I want to define a new macro FOO as follows: #define FOO(x,y) FOO2(x,y) #define FOO(x,y,z) FOO3(x,y,z) But this do...