The Shape of Code

B is for BASIC, Babbage, BCPL, B, BLISS and BLooP

BASIC was the Javascript of its day in the sense that it was the language supported by the greatest number of computing platforms in the field; this is likely a very different view of BASIC than the one readers brought up on the various Microsoft products have. Back in the day Basic (lower case to separate it from its original beginners roots) was a language that met a few simple criteria: 1) it could be implemented in a few K of memory and support useful programs that ran in a few more K, 2) it used line numbers for control flow and source editing, 3) it had a print statement and 4) if it supported arrays they were defined using the letter sequence DIM.

Babbage crossed my path during my first job after graduating. It was billed as a high level assembler, but I suspect it was created as a side project by somebody wanting to learn a bit about compilers who found existing languages too hard. Such languages and their implementations continue to proliferate today, but back in the day developers often had to use them for production work because no alternatives were available.

BCPL was a return to simplicity compared to the increasingly ornate languages that designers were coming up with later in the 1960s. These days it is probably best known, if known at all, as the language that most strongly influenced the design of C. I have found that mentioning its name often brings back fond memories in those who used it in an earlier life.

B was the language designed by the group of guys that came up with C some months later. Its main claim to fame is as a source of debate about whether the successor to C should be called P (the third letter in BCPL) or D (the fourth letter of the alphabet).

BLISS is another systems language from the late 60s. Its claim to fame is as the target language of the PQCC project (Production Quality Compiler-Compiler). This project invented, or at least brought all the pieces together in one place, the structure of how compilers are written today, i.e., convert the source to a tree and have lots of passes walk over this tree slowly transforming it to optimized code. PQCC happened in the early 70s and when I encountered it on a compiler project at Intermetrics at the start of the 80s the design approach seemed impractical to me, and others new to the ideas; the resulting compiler would easily exceed the available computer memory capacity of the day (the secret sauce that rarely got talked about was software memory management). By the mid-90s memory was so plentiful that all the compiler research from the last two decades could finally fly.

BLooP is a language that is not Turing complete. It was created by Douglas Hofstadter for his book Gödel, Escher, Bach and fails to be Turing complete in a rather interesting way, by being limited to computing functions that are primitive recursive.

Things to read

The Design of an Optimizing Compiler, by William Wulf, Richard K. Johnson, Charles B. Weinstock, Steven O. Hobbs, and Charles M. Geschke (longish technical report).

I suspect “Gödel, Escher, Bach” got such rave reviews in its day because nobody wanted to admit to not understanding it; I found it overly long and too full of itself. Chunks of it might appeal to a young audience.