jmckitrick / maru Goto Github PK

(On Linux, type "make".  On Darwin, edit the first line of emit.l to
set __MACH__ to anything other than () then type "make".  MinGW has
library issues and doesn't work -- sorry.)

This is a metacircular evaluator for an s-expression language, plus a
"level shift" from s-expressions down to IA32 machine code to escape
the infinite metacircular regress.

boot-eval.c contains a reader/evaluator for the s-expression language,
written in C.  eval.l contains the same evaluator, written in the
s-expression language.  emit.l contains a compiler from s-expressions
to IA32 machine code, written in the s-expression language.  boot.l
contains some data structures and algorithms needed by emit.l, written
in the s-expression language.

boot-eval.c is compiled and then run on boot.l+emit.l+eval.l to create
eval.s, a machine code implementation of the s-expression evaluator.
eval.s is then assembled and linked to make eval, which can be run on
boot.l+emit.l+eval.l to create eval.s.  The C compiler is then
entirely out of the loop (unless you lose a working evaluator and need
to bootstrap again).

The s-expression language has a few interesting characteristics.  You
can get a feeling for some of them by looking how messaging and
multimethods are implemented.  The compiler makes some attempt to be
small and simple (1750 loc for all three ".l" files, including some
debugging cruft that could be removed) and no attempt whatsoever to
optimise. Even so, the generated code runs at 40% the speed of
aggressively-optimised C on my E5430, measured by the convenient macro
benchmark: dividing the run time of regenerating eval.s via eval by
that of generating it initially via boot-eval.