Overview of Materials in Cycles - Blender Cycles Materials and Textures - page 15

The effect of the Wave Texture assigned as color to the Glossy component of the material
6. Disconnect the texture color output from the Glossy shader. Grab and connect
the texture node's Fac output to the Roughness input socket of the Glossy BSDF
shader, as shown in this screenshot:
The effect of the Wave Texture assigned as Roughness factor to the Glossy component of the material