OpenCL : invalid operands to binary expression

Hi Everybody,
       I have a problem when parsing opencl kernel source file.

I have vector type varaibles, such as float3.

float3 x ;
float3 y;
float3 z;
//some inital work

z = x + y;

here compiler will complain : error: invalid operands to binary expression

Does anybody know how to solve this problem ?