Syntax errors are a problem because there is no fixed syntax. (And I am sorry I don't have the energy to explain this problem the umpteeth time.)
On Nov 17, 2010, at 5:23 PM, Ryan Culpepper wrote: > Syntax has dependencies. In (X . ARGS), the interpretation of ARGS depends on > X. So X should be validated* before ARGS is interpreted. Most macros either > obey this principle automatically or have relatively benign violations**, but > #%app is a bit special. > > I agree with Carl. > > Ryan > > * Probably X doesn't need to be fully validated, just enough to justify the > decisions based on it. > > ** Here's a benign violation: > > (rwhen body condition) => (when condition body) > > If both body and condition contain syntax errors, the error in condition is > reported first, surprisingly. A slightly better way to write the macro would > be this: > > (rwhen body condition) => (let ([c (lambda () condition)]) > (when (c) body)) > > Expansion happens in the expected order, and the compiler can fix up the code > afterwards. > > > On 11/17/2010 02:19 PM, Matthias Felleisen wrote: >> >> That's a fix for the symptom, and it occurred to me too. >> Let's try to look at the large picture, too, instead of >> just looking for bandaids for symptoms. >> >> >> On Nov 17, 2010, at 4:17 PM, Carl Eastlund wrote: >> >>> Personally I would like to see the error here be that >>> define-struct/contract is not bound. If the order of either top level >>> expansion or #%app worked slightly differently, we could get that >>> error first and all would be clear. >>> >>> Carl Eastlund >>> >>> On Wed, Nov 17, 2010 at 4:15 PM, Matthias Felleisen >>> <matth...@ccs.neu.edu> wrote: >>>> >>>> Isn't the true problem that we pretend uniformity of syntax and values? In >>>> this case, we specifically pretend that functions and syntaxes may consume >>>> the same kind of keyword-labeled arguments. Except that when you make a >>>> small mistake, the brittleness of this arrangement shows up and you get >>>> WEIRD ERROR MESSAGES. >>>> >>>> When systems work, nobody cares how they work. It's errors that make >>>> people notice, and errors happen all the time. >>>> >>>> >>>> >>>> On Nov 17, 2010, at 3:55 PM, Jon Rafkind wrote: >>>> >>>>> I found this error message confusing. The problem is I forgot to require >>>>> racket/contract. >>>>> >>>>> #lang racket/base >>>>> >>>>> (define-struct/contract foo ([a any/c]) #:transparent) >>>>> >>>>>> >>>>> application: missing argument expression after keyword at: #:transparent >>>>> in: (#%app define-struct/contract foo ((a any/c)) #:transparent) >>>>> >>>>> I was confused because I thought I had a (require racket/contract) >>>>> somewhere but apparently I didn't. I don't know if anything at all can >>>>> be done about it.. >> >> _________________________________________________ >> For list-related administrative tasks: >> http://lists.racket-lang.org/listinfo/users > _________________________________________________ > For list-related administrative tasks: > http://lists.racket-lang.org/listinfo/users _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
