The phantasies of computer scientists in the 1960s knew no bounds. Spurned by the
success of automatic syntax analysis and parser generation, some proposed the idea of the
flexible, or at least extensible language. The notion was that a program would be
preceded by syntactic rules which would then guide the general parser while parsing the
subsequent program. A step further: The syntax rules would not only precede the
program, but they could be interspersed anywhere throughout the text. For example, if
someone wished to use a particularly fancy private form of for statement, he could do so
elegantly, even specifying different variants for the same concept in different sections of
the same program. The concept that languages serve to communicate between humans
had been completely blended out, as apparently everyone could now define his own
language on the fly. The high hopes, however, were soon damped by the difficulties
encountered when trying to specify, what these private constructions should mean. As a
consequence, the intreaguing idea of extensible languages faded away rather quickly.