m4: History
1.2 Historical references
=========================
Macro languages were invented early in the history of computing. In the
1950s Alan Perlis suggested that the macro language be independent of
the language being processed. Techniques such as conditional and
recursive macros, and using macros to define other macros, were
described by Doug McIlroy of Bell Labs in "Macro Instruction Extensions
of Compiler Languages", _Communications of the ACM_ 3, 4 (1960), 214-20,
<http://dx.doi.org/10.1145/367177.367223>.
An important precursor of 'm4' was GPM; see C. Strachey, "A general
purpose macrogenerator", _Computer Journal_ 8, 3 (1965), 225-41,
<http://dx.doi.org/10.1093/comjnl/8.3.225>. GPM is also succinctly
described in David Gries's book _Compiler Construction for Digital
Computers_, Wiley (1971). Strachey was a brilliant programmer: GPM fit
into 250 machine instructions!
Inspired by GPM while visiting Strachey's Lab in 1968, McIlroy wrote
a model preprocessor in that fit into a page of Snobol 3 code, and
McIlroy and Robert Morris developed a series of further models at Bell
Labs. Andrew D. Hall followed up with M6, a general purpose macro
processor used to port the Fortran source code of the Altran computer
algebra system; see Hall's "The M6 Macro Processor", Computing Science
Technical Report #2, Bell Labs (1972),
<http://cm.bell-labs.com/cm/cs/cstr/2.pdf>. M6's source code consisted
of about 600 Fortran statements. Its name was the first of the 'm4'
line.
The Brian Kernighan and P.J. Plauger book _Software Tools_,
Addison-Wesley (1976), describes and implements a Unix macro-processor
language, which inspired Dennis Ritchie to write 'm3', a macro processor
for the AP-3 minicomputer.
Kernighan and Ritchie then joined forces to develop the original
'm4', described in "The M4 Macro Processor", Bell Laboratories (1977),
<http://wolfram.schneider.org/bsd/7thEdManVol2/m4/m4.pdf>. It had only
21 builtin macros.
While 'GPM' was more _pure_, 'm4' is meant to deal with the true
intricacies of real life: macros can be recognized without being
pre-announced, skipping whitespace or end-of-lines is easier, more
constructs are builtin instead of derived, etc.
Originally, the Kernighan and Plauger macro-processor, and then 'm3',
formed the engine for the Rational FORTRAN preprocessor, that is, the
'Ratfor' equivalent of 'cpp'. Later, 'm4' was used as a front-end for
'Ratfor', 'C' and 'Cobol'.
René Seindal released his implementation of 'm4', GNU 'm4', in 1990,
with the aim of removing the artificial limitations in many of the
traditional 'm4' implementations, such as maximum line length, macro
size, or number of macros.
The late Professor A. Dain Samples described and implemented a
further evolution in the form of 'M5': "User's Guide to the M5 Macro
Language: 2nd edition", Electronic Announcement on comp.compilers
newsgroup (1992).
François Pinard took over maintenance of GNU 'm4' in 1992, until 1994
when he released GNU 'm4' 1.4, which was the stable release for 10
years. It was at this time that GNU Autoconf decided to require GNU
'm4' as its underlying engine, since all other implementations of 'm4'
had too many limitations.
More recently, in 2004, Paul Eggert released 1.4.1 and 1.4.2 which
addressed some long standing bugs in the venerable 1.4 release. Then in
2005, Gary V. Vaughan collected together the many patches to GNU 'm4'
1.4 that were floating around the net and released 1.4.3 and 1.4.4. And
in 2006, Eric Blake joined the team and prepared patches for the release
of 1.4.5, with subsequent releases through intervening years, as recent
as 1.4.18 in 2016.
Meanwhile, development has continued on new features for 'm4', such
as dynamic module loading and additional builtins. When complete, GNU
'm4' 2.0 will start a new series of releases.
Info Catalog
m4: Intro
m4: Preliminaries
m4: Bugs