The XPL programming language is a derivative of PL/I designed for compiler writing. XPL was first announced at the 1968 FJCC in San Francisco, CA. (See McKeeman, Horning, Nelson and Wortman below.)
XPL is the name of both the programming language and the compiler generator system (or TWS: translator writing system) based on the language.
More info here: http://www.cs.toronto.edu/XPL/
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Moshix
September 2021