[plt-scheme] check-expect not allowed in expression position?

On Wed, Mar 31, 2010 at 1:41 AM, Danny Yoo <dyoo at cs.wpi.edu> wrote:
> I was trying to use test-engine's check-expect to write a test case,
> and I found myself wanting to use it in an expression position.  I
> came across the error:
>
>    check-expect: found a test that is not at the top level
>
> I understand that, as a mechanism, all the test cases are
> syntactically re-adjusted so that they're valid even if they're
> referring to definitions defined after the tests.  However, I thought
> I might try to work around the limitation with the following macro.
> The idea of my macro is to rearrange things enough to make
> check-expect happy, but it doesn't work:
>
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
> (define-syntax (check-expect* stx)
>  (syntax-case stx ()
>    [(_ observed expected)
>     (with-syntax ([observed-thunk
>                    (syntax-local-lift-expression #'#f)]
>                   [expected-thunk
>                    (syntax-local-lift-expression #'#f)])
>       (begin
>         (syntax-local-lift-module-end-declaration
>          (syntax/loc stx
>            (check-expect (observed-thunk) (expected-thunk))))
>         (syntax/loc stx
>           (begin
>             (set! observed-thunk (lambda () observed))
>             (set! expected-thunk (lambda () expected))
>             (void)))))]))
> ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
>
>
> After seeing the error, I now understand that I misused
> syntax-local-lift-module-end-declaration, which says that, in the way
> I'm using it, eventually the thing being lifted will be expanded in
> expression context.  Of course, this isn't what I want: I want to lift
> a syntax up to the module or top-level context.  I can't find the
> right primitive that does this.  Am I missing something obvious?

Danny,

I resolved the issue of check-expect's context in Dracula by basically
reimplementing the logic of check-expect.  Mine works in any
definition context (internal as well as top-level and module), but
could easily be adapted to expressions as well.  You can find the
source code at:

http://planet.plt-scheme.org/package-source/cce/dracula.plt/8/10/teachpacks/testing.ss

--Carl