Melt the butter in a saucepan. Remove from heat, stir in flour and seasonings. Add a little milk and stir to blend. Gradually stir in the remaining milk. Cook and stir until mixture boils and thickens. Add shrimp (or clams or chicken) and pineapple tid-bits. Heat through. Serve over hot cooked rice. If desired, serve with condiments such as chopped peanuts, coconut or chutney.