GLSL function default parameter

I am trying to compile a function with a default parameter:

mat3 id3(float w = 1.0) { return mat3(w, 0.0, 0.0, 0.0, w, 0.0, 0.0, 0.0, w);}

But the compiler is saying:

ERROR: 0:203: error(#132) Syntax error: "=" parse error

Any idea ? Are default parameters not available with the AMD GLSL compiler ?

Thanks