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Date: Mon, 14 Feb 2000 11:49:27 GMT
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From: John Harper <john@dcs.warwick.ac.uk>
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To: "Mikolaj J. Habryn" <dichro-mail-682f458@rcpt.to>
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Subject: Re: embedding librep
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Mikolaj J. Habryn writes:
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| Hi John - do you have any simple examples of using librep in an
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|inferior role? I need a scripting interface for a program that I'm
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|writing, and I'd much rather re-use somebody else's code :) Is there
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|anything other than sawmill (or presumably jade) that I could squint
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|at and try to understand?
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the simplest (and only other) example is rep.c in librep/src, it's not
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commented so here's a slightly simplified annotated version (from cvs
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-- this boots the lisp environment, then loads the rep.jl[c] script
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return rep_load_environment (rep_string_dup ("rep"));
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main(int argc, char **argv)
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char *prog_name = *argv++;
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-- this initialises the lisp data structures
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rep_init (prog_name, &argc, &argv, 0, 0);
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if (rep_get_option ("--version", 0))
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printf ("rep version %s\n", REP_VERSION);
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-- this function is complex, it creates an execution context
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then calls inner_main from within this new context. It's
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needed because new librep does continuations and (soft)
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rep_call_with_barrier (inner_main, Qnil, rep_TRUE, 0, 0, 0);
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-- this function just checks if an error occurred, if so it
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will print some descriptive message, and returns a suitable
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return rep_top_level_exit ();
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But this is only half the story (or less). The main thing you'd have to
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understand is the C representation of Lisp data types. The header file
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rep_lisp.h defines this, and is reasonably well commented. For each
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data type there will be at least two macros rep_FOOP (x) which tests
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if a repv (a lisp pointer) is of type FOO, and rep_FOO (x) which casts
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the lisp pointer to the correct C pointer.
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So, e.g. for pairs, there's rep_CONSP and rep_CONS. There's also
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accessor macros rep_CAR (x) and rep_CDR (x) for this type.
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Another thing is that if a repv == rep_NULL, then an error occurred
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somewhere, and control should be unwound back to the top-level
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Garbage collection also complicates things, I posted a message to
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librep-list explaining the mechanics of this, it will be in the
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archives on sourceforge..
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I've been meaning to document all this, but it's quite an undertaking :-)
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If you decide to use rep, I'm happy to answer as many questions as you
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have, or just post them to librep-list@lists.sourceforge.net
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