On 03/29/2010 09:45 PM, Jon Rafkind wrote:
On 03/29/2010 03:19 PM, Matthew Flatt wrote:
At Mon, 29 Mar 2010 15:06:00 -0600, Jon Rafkind wrote:
Can these error messages be reviewed as well?
On 03/26/2010 03:55 PM, Jon Rafkind wrote:
Can this error message
illegal use of syntax
be changed to
illegal application of a transformer. transformers must be
functions
that accept one argument.
To reproduce this error use this code:
(define-syntax (foo a b c) #'1)
(foo)
There is only one change to be made in eval.c line ~6284
Like the suggested `syntax-case' change, I think this one assumes the
perspective of a macro implementor with a particular goal.
In general, an identifier bound with `define-syntax' doesn't have to be
bound to a transformer procedure. A non-transformer binding may be
intentional and useful, such as when a pattern variable is bound by
`syntax-case'.
In such cases, it's a good idea to make the binding also include a
transformer procedure (perhaps through `prop:procedure') and refine the
"illegal use of syntax" error message --- just like it's a good idea to
cover more cases in `syntax-case' or `syntax-parse' and give good error
messages. But if a programmer doesn't do that, then "bad syntax" or
"illegal use of syntax" is about all that can be said automatically.
I don't follow you. The C code has a check to see if the thing being
applied is a procedure with an arity of 1. If it is anything else, the
error "illegal use of syntax" will be raised. So my suggestion is for
the error message to mirror the check being done.
Here is some simple code that throws a nicer error for macros when they
are used incorrectly. Probably not useful enough for planet, so I'll
just post it here in case anyone is interested. This works correctly
with `syntax-local-value'.
macro-data.ss:
#lang scheme
(provide (all-defined-out))
(define-struct macro (name function) #:property prop:procedure
(lambda (self . args)
(let ([function (macro-function self)])
(if (not (procedure-arity-includes? function (length
args)))
(raise-syntax-error (macro-name self) "wrong
number of arguments supplied" args)
(apply function args)))))
define-syntax.ss:
#lang scheme
(require (for-syntax scheme/base
"macro-data.ss"))
(require (prefix-in original: (only-in scheme/base define-syntax)))
(define-syntax (define-syntax stx)
(syntax-case stx ()
[(_ (id args ...) expr0 expr ...)
#'(original:define-syntax id (make-macro 'id (lambda (args ...)
expr0 expr ...)))]
[(_ (id args ... . rest-args) expr0 expr ...)
#'(original:define-syntax id (make-macro 'id (lambda (args ... .
rest) expr0 expr ...)))]
[(_ rest ...)
#'(original:define-syntax rest ...)]))
Then just (require "define-syntax.ss") and away you go.
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