<fabricemarchant@free.fr> wrote:
+---------------
| >  I can send you an original "siod.1.3.c",
| I'm interested with this, thanks !
+---------------

[Done.]

+---------------
| >- You're not going to learn much new from looking at anything
| >  earlier than 1.3, since 1.3 is the first one that says
| >  "define now works properly". (!!)
| That sounds very bad indeed.
+---------------

Why "bad"?!? SIOD 1.0 was a one-afternoon hack, as the documentation
is quite explicit about:

    http://people.delphiforums.com/gjc/siod.html#apology
    Apology, discussion and motivation
    ...
    Defining and executing fib resulted in a code-coverage of over
    95% of the lines of the C program. Hence, SIOD, Scheme in One Day.

I see nothing wrong in taking only a week more to make DEFINE "work
properly".

+---------------
| >- You're not going to learn much new from looking at 1.3
| >  that you wouldn't learn from a somewhat later, more featureful
| >  version such as 2.7 [May 1992] or even 3.4 [May 1997].
| I think : older -> simpler -> easier to study and understand !
| The reason I was interested in 1.0 is it doesn't implement macro.
| So I hoped the sources are lighter.
+---------------

Given that the source says that macros [and LOAD, and predicates!]
were added in 1.1, just one *day* later than 1.0, my guess is that
1.0 is practically useless, except for running his initial FIB demo.

Look, macros are practically trivial to implement, yet without them
it's a horrible pain to implement the *rest* of the language. No Lisp
or Scheme without them is "real".

Specifically, in SIOD 1.3 the implementation of macros is a 4-line hack
in EVAL, namely, if the value of a variable in function position of a
form is itself a *symbol* [rather than a function], then EVAL assumes
that that symbol names a macro function, calls it with the form, and
then loops to re-evaluate the result[*]:

    ...
    case tc_cons:
      tmp = leval(CAR(x),env);
      switch TYPE(tmp) {
	 ...[all the other usual cases]...
[*]==>	 case tc_symbol:
[*]==>	   x = cons(tmp,cons(cons(sym_quote,cons(x,NIL)),NIL));
[*]==>	   x = leval(x,NIL);
[*]==>	   goto loop;
	 default:
	   err("bad function",tmp);}
    ...

That's it. Really. Out of the total of 1147 lines of source code,
those 4 are all it took to implement macros [at least, the kind
that SIOD has].


-Rob

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