Lessons From PL/I: A Most Ambitious Programming Language
fliptop writes:
PL/I stands for Programming Language 1, and its aim was to be the Highlander of programming languages:
...there would be no need for 2, 3, or 4 if everything went to plan. While it is clear today that goal was never reached, what might not be evident is that what PL/I was trying to achieve was a pretty reasonable idea, or at least not entirely crazy. What also wasn't evident at the time was how enormously difficult that reasonable idea turned out to be.
PL/I was designed by IBM with the goal of bringing together the power of 3 different programming languages: FORTRAN (1954), ALGOL (1958), and COBOL (1959).
On paper, this makes a lot of sense. Computer programming can be difficult, and why should there be multiple programming languages? And because computer programming of the era required a lot of punched cards, having One Good Programming Language would have on paper (or cardboard) benefits to simplify the process of development as well. Work on the PL/I specification started in 1964, and work on the first compiler in 1966.
[...] But PL/I wasn't just a development effort, it was also in effect a system conversion. There was an explicit goal for developers to start using PL/I, but were also implicit goals for developers not just to only stop using FORTRAN, COBOL, and ALGOL directly, as well as to convert their existing solutions and codebases to PL/I. As if that wasn't hard enough, compounding the problem was that FORTRAN, COBOL, and ALGOL were all evolving in real time. As I described in my BLOG@CACM post "The Art of Speedy Systems Conversions," a system conversion is one of the most difficult things to do in software engineering. The existing system typically has massive head start, and the replacing system needs to start up development, accelerate, reach feature parity, and then both systems need to be stable long enough to make the switch.
The author presents development timelines of COBOL, FORTRAN and ALGOL showing development on these languages was active for years after PL/I development had started. The historical verdict?
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