Mix together sugar, corn syrup, cream, and salt; let stand about 20 minutes. When sugar is dissolved, place on heat and bring quickly to a boil. When almost at the soft-ball stage, remove from heat and stir in persimmon pulp and butter. Return to heat and boil, stirring constantly until it reaches the soft-ball stage. Remove from heat and leave until partly set, then beat until mixture shows signs of hardening. Pour onto buttered plate and mark into squares when cooled.