Combine cherries, tapioca and sugar in a sauce pan. Cook 10 minutes.
Combine cornstarch and water. Stir into pan.
Beat egg yolks and add to mixture. Cook 2 minutes. Stir in vanilla.
Chill and serve with vanilla ice cream, frozen yogurt, or eat plain.
* If you prefer to use sweet cherries, reduce sugar by 1/2 cup.