- mapping-intern mapping key failureprocedure
Extracts the value associated to key in the mapping mapping, and returns mapping and the value as two values. If key is not contained in mapping, failure is invoked on no arguments. The procedure then returns two values, a newly allocated mapping that uses the same comparator as the mapping and contains all the associations of mapping, and in addition a new association mapping key to the result of invoking failure, and the result of invoking failure.