Re: [TUHS] History of m6?

M6 originated as a porting tool for the Fortran source code for Stan Brown's Altran language for algebraic computation. M6 itself was originally written in highly portable Fortran. Arnold asked, "How widespread was the use of macro processors in high level languages? They were big for assembler, and PL/1 had a macro language, but I don't know of any other contemporary languages that had them." Understanding "contemporary" to mean pre-C, I agree. Cpp, a particularly trivial macroprocessor, has been heavily used ever since--even for other languages, e.g. Haskell. The rumor that Bob Morris invented macros is off the mark. Macros were in regular use by the time he joined Bell Labs. He did conceive an interesting "form-letter generator", called "form", and an accompanying editor "fed". A sort of cross between macros and Vannevar Bush's hypothetical memex repository, these were among the earliest Unix programs and appeared in the manual from v1 through v6. Off-topic warning: pre-Unix stories follow. Contrary to an assertion on cat-v.org, I did not invent macros either. In 1959 Doug Eastwood and I, at the suggestion of George Mealy, created the macro facility for SAP (SHARE assmbly program) for the IBM 704. However, the idea was in the air at the time. In particular, we knew that GE already had macros, though we knew no details about their syntax or semantics. There were various attempts in the 1960s to build languages by macro extension. The approach turned out to entail considerable social cost: communication barriers arise when everyone can easily create his own dialect. A case in point: I once had a bright young mathematician summer employee who wrote wonderfully concise code by heaping up macro definitions. The result was inscrutable. Macros caught on in a big way in the ESS labs at Indian Hill. With a macro-defined switching language, code builds were slow. One manager there boasted that his lab made more thoroughgoing use of computers than other departments and cited enormous consumption of machine time as evidence. Steve Johnson recalls corrrectly that there was a set of macros that turned the assembler into a Lisp compiler. I wrote it and used it for a theorem-proving project spurred by Martin Davis. (The project was blown away when Robinson published the resolution princple.) The compiler did some cute local optimization, taking account of facts such as Bob Morris's astute observation that the 704 instruction TNZ (transfer on nonzero) sets the accumulator to zero. Doug