XPL

XPL, short for expert's programming language, is a programming language based on PL/I designed in 1967 by William M. McKeeman, David B. Wortman, James J. Horning and others at Stanford University, first announced at the 1968 Fall Joint Computer Conference. It came bundled with a portable one-pass compiler written in XPL itself and a parser generator tool, together forming a self-contained kit for building compilers for other languages. XPL was created specifically to teach compiler design and to give students a practical starting point for writing compilers of their own, rather than to serve as a general application-programming language. It follows a procedural, structured and systems-programming style, and was distributed as open source through the IBM SHARE users organization, which let the design spread widely through university compiler courses.