Heirloom Software: the Past as Adventure

ADVENT was artistically innovative—and with an architecture ahead of its time as well. Though the possibility had been glimpsed in research languages (notably LISP) as much as a decade earlier, ADVENT is one of the earliest programs still surviving to be organized as a complex, declaratively specified data structure walked by a much simpler state machine. This is a design style that is underutilized even today.

The continuing relevance of ADVENT's actual concrete source code, on the other hand, is quite a different matter. The implementation aged much more rapidly—and badly—than the architecture, the game or its prose.

ADVENT was originally written under TOPS-10, a long-defunct operating system for the DEC PDP-10 minicomputer. The source for the original version still exists (you can find it and other related resources at the Interactive Fiction Archive, but it tends to defeat attempts to appreciate it as a work of programming art because it's written in an archaic dialect of FORTRAN with (by actual count) more than 350 gotos in its 2.4KLOC of source code.

Preserving that original FORTRAN is, therefore, good for establishing provenance (as historians think about these things) but doesn't do a whole lot for that I've suggested as the cultural purposes of keeping these artifacts around. For that, a faithful translation into a more modern language would be far more useful.

As it happens, Don Woods' 1977 version of ADVENT was translated into C less than two years after it was written. You can still play it—and read the code—as part of the BSD Games package. Alas, while that translation is serviceable for building and running the program, it's not so great for reading. It is less impenetrable than the FORTRAN, but was not moved fully to idiomatic C and reads a bit strangely to a modern eye. (To be fair to the translators, the C language was still in its childhood in 1977, and its modern idioms weren't all that well developed yet.)

Thus, there are still a forbidding number of gotos in the BSD translation. Lots of information is passed around through shared globals in a way that was typical in FORTRAN but was questionable style in C even then. The BSD C code is full of mystery constants inherited from the ancestral FORTRAN source. And there is a serious comprehensibility problem around the custom text database that both the original FORTRAN and BSD C versions used—a problem I'll return to later in this article.

Through the late 1970s and early 1980s a lot of people wrote extensions of ADVENT, adding more rooms and treasures. The history of those variants is complicated and difficult to track. Almost lost in the hubbub was that the original authors—Will Crowther and Don Woods—continued to revise their game themselves. The last mainline version—the last release by Don Woods—was Adventure 2.5 in 1995.

I found Adventure 2.5 in the Interactive Fiction Archive in late 2016. Two things caught my attention about it. First, I had not previously known that Crowther and Woods themselves had shipped a version so extended from the famous original. Second—and unlike the early BSD port—there was nothing resembling what we'd expect in a modern source release to go with the bare code and the Makefile. No manual page. No licensing statement.

Furthermore, the 2.5 code was deeply ugly. It was C, but in worse shape than the BSD port. The comments actually included an apology from Don Woods explaining that it had been mechanically lifted from FORTRAN by a homebrew translator of his own devising—and apologizing for the bad style.

Nevertheless, I saw a possibility—and I wrote Don asking his permission to ship a cleaned-up version under a true open-source license. The reply was some time in coming, but Don not only granted permission speaking for both himself and Will Crowther, he also actively encouraged me to do this thing.

Now a reminder about what I think the goals of heritage preservation ought to be: I felt it was essential that the cleaned-up version should at no point break functional compatibility with what we got from Woods and Crowther. Therefore, the very first thing I did after getting the heirloom source to build clean was add the ability for it to capture command logs for regression testing.

When you do a restoration like this, it's not enough merely to make a best effort to preserve original behavior. You ought to be able to prove you have done so. Best practice, then is to start by building a really comprehensive set of regression tests. And that's what I did.

What we did, I should say. The project quickly attracted collaborators—most notably Jason Ninneman. The first of Jason's several good ideas was to use coverage-analysis tools to identify gaps in the test suite. Later, Petr Vorpaev, Peje Nilsson and Aaron Traas joined in. By about a month from starting, we could show more than 95% test coverage. And, of course, we ran retrospective testing with the newest version of the test suite on the earliest version we could make read the logs.

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