Hi there,
I am currently trying to write an enhanced version of an interpreter
for a little language I am developing. For that, I would like to be
able to (a) pass a list containing symbols of my language's keywords
to an interpret-function; this function should let-define
implementations for the keywords and then evaluate the list using
those procedure bindings. And (b) I would like to do something similar
with macros.
First, something that is close to what I want to do and what works:
(define (interpret)
(let
[(myadd +) (mymul *)]
(myadd 4 (mymul 5 2
(display (interpret))
This procedure returns 14, as expected. Now, instead of hardcoding the
program into evaluate, I want to pass it as an parameter. As in:
(define (interpret prog)
(let
[(myadd +) (mymul *)]
(eval prog)))
(display (interpret '(myadd 4 (mymul 5 2
This, however, results in Error: unbound variable: mymul. I also tried
to pass different environments to eval, but that didn't seem to make
any difference? How can I convince eval to use the locally bound
procedures?
To go even one step further (assuming, that the above example worked),
I would like to be even able to exchange some of the function
definitions in the evaluate with a define-syntax. However, this define-
syntax should be scoped to the evaluate procedure. The (non-working)
example would look like this, then:
(define (interpret prog)
(define-syntax myadd
(syntax-rules ()
([_ params] (+ params
(let
[(mymul *)]
(eval (macro-expand prog
(display (interpret '(myadd 4 (mymul 5 2
In my brain, this should result in the prog being expanded such that
the myadd-keyword is replaced by the + (that is, the myadd
implementation is being inlined). The mymul keyword would be a
reference to the * function. Here it wouldn't be a big difference, but
for more complicated keywords, there might be a tradeoff between
doing a lot of inlining of frequently used but short keywords and just
referencing long or infrequently used functions.
The scoping of the macros would be important, because there might be
an additional analyse function that expands the program using
different macros with the same names. The only reference I found, that
macros can be scoped, is here on the very bottom of the page: http://community.schemewiki.org/?scheme-faq-macros
But that didn't help me either.
Maybe this is something really stupid and can be solved by some clever
quasi-quoting and unqouting or something (oh, and if possible I would
like to try to solve that without additional libraries, if possible);
but I really tried hard and searched the net and everything and just
can't see what I am missing here... So your help would be greatly
appreciated:)
Thanks,
Christoph
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