The structure and components of the first programming languages were dictated by the architecture of computers. It was the human mind which had to bend to the peculiarities of the machine. When basic technical problems were solved a reverse current began to get stronger. There began a search for formalisms which would allow to program computers on a high and expressive level of abstraction. One effect of the search was the birth of those programming languages which we call declarative. From the beginning there have been two main streams in the field of declarative programming: functional...