Place cornstarch and paprika in a plastic bag. Shake a few pieces of chicken at a time in bag with cornstarch and paprika. Save left over cornstarch for sauce mixture. Brown chicken slowly in a moderately hot skillet, turning as necessary. When lightly browned 15 to 20 minutes, reduce heat, cover tightly, and cook slowly until almost tender 10 to 20 minutes. Drain pineapple, saving liquid. Add pineapple, celery, and green pepper and add to pan, and place chicken pieces over the top of the vegetables. Cover and cook for five minutes. Combine 1 tablespoon of cornstarch with the remaining of the cornstarch mixture that was used to coat the chicken, and add brown sugar, cornstarch, soy sauce, and 1/4 cup pineapple liquid. Pour over chicken. Cover and continue to cook for 10 minutes. Stir walnuts and raisins into mixture and serve with cooked rice.