[r6rs-discuss] Proposed features for small Scheme, part 9: modules
cowan at ccil.org
Mon Oct 12 12:54:54 EDT 2009
Brian Harvey scripsit:
> Personally, I couldn't care less about modules -- I'd be happy for WG1
> Scheme not to have them -- but it's very important to me that there
> be no such idea as "macro-time" or "compile-time" or anything-time in
> WG1 Scheme. There is only REPL-time.
With the exception of SCM, all implementations of R5RS that I know of,
including both interpreters and compilers, expand macros in a top-level
form before executing the resulting code. Not doing so makes macro
hygiene very difficult. SCM is able to avoid doing so because it has
first-class lexical environments, which other implementers seem to
believe are a cure worse than the disease.
In a REPL, of course, there is a continual alternation between macro
expansion time and run time as new forms are entered. In particular,
however, if you write
(defun x (include "three.scm"))
where the file "three.scm" contains simply the single character 3,
this is the same as writing
(defun x 3)
Note that the argument to include must be a string literal, and cannot
be an arbitrary string-valued expression; this limitation does not apply
John Cowan cowan at ccil.org http://ccil.org/~cowan
Female celebrity stalker, on a hot morning in Cairo:
"Imagine, Colonel Lawrence, ninety-two already!"
El Auruns's reply: "Many happy returns of the day!"
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