Combine the sugar, corn syrup, water and salt in a saucepan. Cook and stir over medium heat until the mixture starts to boil. Continue coking until the mixture forms a soft ball when tested in cold water (or use a thermometer 240 degrees). Beat the egg whites until stiff. Then pour 1/2 cup of the syrup over the whites, beating quickly at all times.
Continue to cook the remaining syrup while beating the egg whites, until the syrup reaches the light crack stage when dropped in cold water (this happens quickly at 285 degrees). Pour the remaining syrup over the egg white mixture, beating quickly at all times. Continue beating until the candy begins to hold its shape. Stir in the maple extract and nuts. If you prefer, a little food coloring could be added at this time. Drop by teaspoons onto parchment or waxed paper.