Programming language life cycles.

New programming languages keep getting invented, and old languages (most of them) eventually die. Many languages are eventually reduced to, if anything, a single surviving slogan or idea. (Examples: COBOL = programs look like English; SNOBOL = pattern matching on strings.) How do ideas about what programmers want or need to do drive decisions made by language designers? We'll look at some of these ideas, and also at the origin, evolution, and possible destinations of certain ideas pursued during the development of the Fortress programming language, speculating on the forces that drive these life cycles.