Better error message for expand.

[Michael D. Adams]

The error message when running expand on a non-expression is difficult for a new user to understand. It should explain that expand doesn't work on defines unless they are wrapped in "(let () ...)".

> (expand '(define-record-type foo) (environment '(ikarus)))
Unhandled exception
 Condition components:
   1. &error
   2. &who: expander
   3. &message: "invalid expression"
   4. &irritants: ((define #{g0 |58AR2IT9On3HXN9X|} (make-record-type-descriptor 'foo #f #f #f #f '#())))

[Abdulaziz Ghuloum (aghuloum)]

Would new users be using expand? Notice that the error comes from the expander, which is the same error you'd get when you type
  (+ (define-record-type foo) 14)
Would saying "definition found where an expression was expected" be any better?

[Abdulaziz Ghuloum (aghuloum)]

Kind of fixed in revision 1078. Reopen if you have any suggestions.

[Michael D. Adams (mdmkolbe)]

That would definitely be better, since almost everything in Scheme is an expression, "invalid expression" was about as useful as "invalid". My mind is a bit poisoned with the knowledge of why it is invalid, but I can't tell how much better it is, but when it showed the error to Roshan he seemed find it fairly easy to understand.

[Abdulaziz Ghuloum (aghuloum)]

There is, of course, this other problem that the code displayed in
the error message is not the code you originally wrote, but rather,
the code that define-record-type expanded to. THIS needs to be
fixed, but I don't know, yet, the best approach to take.

[Abdulaziz Ghuloum (aghuloum)]

This bug report is about to be closed as the fix comitted previously
will be incorporated in the next 0.0.2 release of Ikarus Scheme,
scheduled for November 28, 2007.
A release candidate tarball is available for download from:
  http://www.cs.indiana.edu/~aghuloum/ikarus/ikarus-0.0.2-rc1.tar.gz
Please do test it if you have the time and report any issues you
might encounter. Thank you very much for your support. Aziz,,,
(Sorry for the duplicates; I'm updating every open bug.)