Re: [Chicken-users] unbound variable: or

[John Cowan]

Michele La Monaca scripsit:

> Gambit has it. Too bad Chicken 4 dropped it.

You're right; I was too hasty.  There are a number of other Schemes
that accept it also.  However, it does not fit into the {define-syntax,
let-syntax, let*-syntax, letrec-syntax} set provided by all post-R4RS
Schemes.

> Let’s say someone had the (bad?) idea to masquerade/embed it in other
> more baroque forms. For example in Chicken you have to write:

Yes, if explicit renaming is available (generally the case except in
Schemes that do syntax-case) then you can simulate it by not renaming
anything.  Syntax-case can sort of simulate it, but not 100% accurately.

I'll have more details on who does what posted later when I get my
suite of Schemes working again: at the moment, some of them have
bit-rotted.

> Define-macro is the most basic, no-frills macro system and the one
> which will give you the most profound understanding of what a macro is
> and is not. Oh, and it is quite powerful. I’ve used Gambit to
> practice. Only when you dominate it, I suggest to move on to
> syntax-rules. The latter works at a higher layer (see below), enforces
> hygiene and introduces you to pattern matching (which is not a macro
> specific topic).

That's like saying you should master assembly language before moving on
to a high-level languge like Scheme, because it gives you the most
profound understanding of what a computer does and is quite powerful.
These things are true, but assembly language and low-level macros
also give you the opportunity not only to shoot yourself in the foot,
but to shoot your users in the foot as well: they will write very
reasonable looking macro calls that just won't work because of the
lack of hygiene.  Gensym-renaming helps with half of hygiene, but
there's nothing you can do in writing your macro to provide for the
other half of it.

-- 
John Cowan          http://www.ccil.org/~cowan        address@hidden
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