From comp.lang.scheme [Re: C to Scheme]

[Scott L. Burson]

   From: Jordan Henderson <jordan@Starbase.NeoSoft.COM>
   Date: Fri, 30 May 1997 22:16:42 -0500 (CDT)
   Newsgroups: comp.lang.scheme

   Dave Hanson seems to indicate that a first pass is trivial, a few hours
   work for him.  Admittedly, it's probably not industrial strength and it's
   missing at least one necessary C feature.  How difficult would it be to
   get full ANSI C?  The run-time libraries would take a little while to get
   them good enough to port real world software, but my first guess estimate
   is that someone could do a fully reliable, complete ANSI C->Scheme in
   6 months in their spare time.

I think this is a little optimistic.  ZETA-C, my C implementation for Lisp
Machines, took closer to 2 years, full time.  Granted, some of that was spent
on performance, and on features that go a little outside the normal definition
of a C implementation (like a C mode for Zmacs and incremental compilation),
but still, I can tell you it's more than 6 months' work.

I presume Dave Hanson was starting not from original C source but from a list
structure representation with C semantics.  That indeed is not very hard.  (He
also said he skipped structures, which are nontrivial to implement
compatibly.)  Add a parser with ANSI-compatible preprocessor, etc. etc. and
the time starts to add up.

-- Scott