Perfect -- thank you!
On Sun, Dec 2, 2012 at 1:34 PM, Ryan Culpepper <r...@cs.utah.edu> wrote: > On 12/02/2012 12:14 PM, Greg Hendershott wrote: >> >> I'd like to write a unit test that a syntax-parse expectation failure >> elicits a certain error message. For instance, I'd do a regexp-match? >> that "something" is present in a message like "expected something". >> >> However it seems that syntax-parse expectation failures don't raise an >> exception. In other words, this will never return 'caught: >> >> (with-handlers ([exn? (lambda (exn) 'caught)]) >> something-that-elicits-a-syntax-parse-expectation-failure) >> >> (At first I'd tried exn:syntax?, and when that didn't work, I checked >> to see if it was any kind of exception. Seems not.) >> >> Is there another way to go about this? > > > No, that's how you do it. For example: > > (require syntax/parse) > > (with-handlers ([exn:fail:syntax? (lambda (e) 'caught)]) > (syntax-parse #'1 [x:id 'id])) > ;; => 'caught > > I suspect that what you actually want to do is test a macro that uses > syntax-parse; in that case, the issue you're running into is that the macro > raises a syntax error at compile time, but the with-handlers doesn't (or > rather, wouldn't) get set up to catch the exception until run time. > > There are two ways to fix the problem. One is to use eval or expand in your > test: > > (define testing-ns (make-base-namespace)) > ;; setup testing-ns > (with-handlers ([exn:fail:syntax? ___]) > (parameterize ((current-namespace testing-ns)) > (expand '(macro-using-syntax-parse ___)))) > > The other way is to wrap the macro call in something that catches the > compile-time exception and produces code that raises a similar run-time > exception: > > (with-handler ([exn:fail:syntax? ___]) > (convert-syntax-error > (macro-using-syntax-parse ___))) > > The syntax-parse tests use the second technique. Here's the definition of > convert-syntax-error from tests/stxparse/setup: > > (define-syntax (convert-syntax-error stx) > (syntax-case stx () > [(_ expr) > (with-handlers ([exn:fail:syntax? > (lambda (e) > #`(error '#,(exn-message e)))]) > (parameterize ((error-print-source-location #f)) > (local-expand #'expr 'expression null)))])) > > Ryan > ____________________ Racket Users list: http://lists.racket-lang.org/users
