You should probably change this so that drdr runs the right tests. Changing the module+ main to module+ test is probably the way to go.
Robby On Fri, Jul 11, 2014 at 5:02 PM, Stephen Chang <[email protected]> wrote: > I merged. Thanks again! > >> the interesting thing is that running > `./racket/bin/raco test pkgs/lazy` seems to pass even when I add a > failing test case such as `(! (eq? 1 2)) => #t`. > That same test will fail as expected if I run it within drracket. > > Thats because lazy currently doesn't use the "test" submodule. Running > "racket pkgs/lazy/tests/lang.rkt" shows all tests passing. > > > On Fri, Jul 11, 2014 at 4:00 PM, Luke Whittlesey > <[email protected]> wrote: >> I just sent a pull request : https://github.com/plt/racket/pull/727 >> >> I added a few simple test cases, but the interesting thing is that running >> `./racket/bin/raco test pkgs/lazy` seems to pass even when I add a failing >> test case such as `(! (eq? 1 2)) => #t`. >> That same test will fail as expected if I run it within drracket. >> >> Thank you all for your time and help. (And thank you for creating such a >> nice community and toolset!) >> >> -Luke >> >> >> >> >> >> >> On Fri, Jul 11, 2014 at 12:02 AM, Spencer Florence >> <[email protected]> wrote: >>> >>> It looks like he has taken those down. But I'm sure he would email a copy >>> if asked (the think is http://pl.barzilay.org/resources.html#classnotes btw) >>> >>> >>> On Thu, Jul 10, 2014 at 8:42 PM, Matthias Felleisen <[email protected]> >>> wrote: >>>> >>>> >>>> There are also Eli's class notes. I don't have a URL handy but I am sure >>>> if you google "Eli Barzilay" and "course" you'll find his notes on the >>>> various levels of lazy (plus homework assignments :-) -- Matthias >>>> >>>> >>>> >>>> >>>> >>>> >>>> On Jul 10, 2014, at 6:41 PM, Stephen Chang wrote: >>>> >>>> > Actually, this is a bug, because the expression in a single-argument >>>> > values call is forced prematurely. >>>> > >>>> > eg, This should not error: >>>> > >>>> > -> (let-values ([(x) (values (error "a"))]) 1) >>>> > ; a [,bt for context] >>>> > >>>> > Just like this does not error. >>>> > >>>> > -> (let-values ([(x y) (values (error "a") (error "b"))]) 1) >>>> > 1 >>>> > >>>> > Lazy Racket is trying to preserve the (values x) == x from Racket, but >>>> > since LR's force is recursive, this is actually impossible without >>>> > breaking the semantics like it's doing now. >>>> > >>>> > Luke, thanks for finding this. If you want to submit a pull request, I >>>> > will merge. (Just drop the first clause in the case-lambda entirely.) >>>> > Maybe some extra tests would be nice as well :) Otherwise if you dont >>>> > have time, let me know and I'll do it. >>>> > >>>> >> Beyond the library documentation, does anyone know if there are any >>>> >> discussions or tutorials that go into the do's and don'ts of using #lang >>>> >> lazy ? >>>> > >>>> > There isnt any. You can check out the Barzilay-Clements paper [1] to >>>> > learn about the motivation behind LR, but otherwise LR should have >>>> > "standard" lazy semantics. >>>> > >>>> > [1]: >>>> > http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1047&context=csse_fac >>>> > >>>> > On Thu, Jul 10, 2014 at 1:15 PM, Luke Whittlesey >>>> > <[email protected]> wrote: >>>> >> Thank you for the in-depth analysis. Very interesting. >>>> >> >>>> >> Following your reasoning, if I edit lazy.rkt and force `values` to use >>>> >> `multiple-values` for the single entry case, the example that was >>>> >> previously >>>> >> broken now works. (I just have no idea if this breaks something else >>>> >> in the >>>> >> process.) >>>> >> >>>> >> at lazy.rkt line:223 >>>> >> replace: >>>> >> (define* ~values >>>> >> (case-lambda [(x) x] [xs (multiple-values xs)])) >>>> >> >>>> >> with: >>>> >> (define* ~values >>>> >> (case-lambda [(x) (multiple-values (list x))] [xs (multiple-values >>>> >> xs)])) >>>> >> >>>> >> >>>> >> I had assumed that a reference to an identifier was delayed, so thanks >>>> >> for >>>> >> showing that this is currently not the case. >>>> >> >>>> >> Beyond the library documentation, does anyone know if there are any >>>> >> discussions or tutorials that go into the do's and don'ts of using >>>> >> #lang >>>> >> lazy ? >>>> >> >>>> >> Thanks, >>>> >> Luke >>>> >> >>>> >> >>>> >> On Thu, Jul 10, 2014 at 6:24 AM, Matthew Flatt <[email protected]> >>>> >> wrote: >>>> >>> >>>> >>> I'm not sure whether to call it a bug or a limitation of `lazy`. >>>> >>> >>>> >>> The `lazy` language doesn't delay a reference to an identifier. As a >>>> >>> result, >>>> >>> >>>> >>> (define x y) >>>> >>> (define y (list 1)) >>>> >>> (car x) >>>> >>> >>>> >>> fails. The case could be made that the right-hand side of the >>>> >>> definition >>>> >>> of `x` should have been a lazy reference to `y`, but that's not what >>>> >>> `lazy` currently does. >>>> >>> >>>> >>> A problem with the current choice is that it interacts badly with >>>> >>> `!`, >>>> >>> especially as used by `letrec-values`. The implementation of >>>> >>> `letrec-values` forces the right-hand side of a binding using `!` to >>>> >>> determine how many values it produces. That works ok when the >>>> >>> right-hand side is produced by `values` on more than one argument, >>>> >>> because `values` produces a special multiple-values result that >>>> >>> leaves >>>> >>> its values unforced after `!`. When `values` get one argument, then >>>> >>> it >>>> >>> just returns the argument.... and that's still ok for something like >>>> >>> `(values (list 1 (/ 0)))`, because the `(/ 0)` expression is lazy. >>>> >>> >>>> >>> In your example, the implicit use of `!` for the right-hand side of >>>> >>> the >>>> >>> A` binding produces `(! (list a B))`. That `B` is not itself treated >>>> >>> as >>>> >>> a lazy expression, so forcing the list to be constructed causes `B` >>>> >>> to >>>> >>> be evaluated early. >>>> >>> >>>> >>> You can make the variable reference lazy by wrapping it with `~`: >>>> >>> >>>> >>> (letrec-values ([(A) (values (list 'a (~ B)))] >>>> >>> [(B) (values (list 'b A))]) >>>> >>> B) >>>> >>> >>>> >>> Again, I don't know that you should have to do that, but it's how >>>> >>> `lazy` is defined at the moment. >>>> >>> >>>> >>> At Mon, 7 Jul 2014 15:06:26 -0400, Luke Whittlesey wrote: >>>> >>>> Hello all, >>>> >>>> I've been playing around with creating circular lists (and learning >>>> >>>> racket >>>> >>>> which has been quite fun), but I'm stumped on why the lazy version >>>> >>>> of >>>> >>>> letrec-values is not producing a promise like the lazy version of >>>> >>>> letrec >>>> >>>> does. With the lazy letrec I can create circular lists, but with the >>>> >>>> lazy >>>> >>>> letrec-values I get #<undefined>. See the example below. >>>> >>>> >>>> >>>> ;;;;;;;;;;;;;;;;; example code ;;;;;;;;;;;;;;;;;;;;;;;;; >>>> >>>> #lang lazy >>>> >>>> >>>> >>>> ;; create a circular list using letrec (this works) >>>> >>>> (define example-working >>>> >>>> (letrec ([A (list 'a B)] >>>> >>>> [B (list 'b A)]) >>>> >>>> B)) >>>> >>>> (displayln "Working Example:") >>>> >>>> (displayln example-working) >>>> >>>> (displayln (!! example-working)) >>>> >>>> >>>> >>>> ; Prints... >>>> >>>> ;Working Example: >>>> >>>> ;(b #<promise:A>) >>>> >>>> ;#0=(b (a #0#)) >>>> >>>> >>>> >>>> ;; create a circular list using letrec-values (this is broken) >>>> >>>> (define example-broken >>>> >>>> (letrec-values ([(A) (values (list 'a B))] >>>> >>>> [(B) (values (list 'b A))]) >>>> >>>> B)) >>>> >>>> (displayln "Broken Example:") >>>> >>>> (displayln example-broken) >>>> >>>> (displayln (!! example-broken)) >>>> >>>> >>>> >>>> ; Prints >>>> >>>> ;Broken Example: >>>> >>>> ;(b (a #<undefined>)) >>>> >>>> ;(b (a #<undefined>)) >>>> >>>> ;;;;;;;;;;;;;;;;; end code ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; >>>> >>>> >>>> >>>> I realize that there are many different ways to generate circular >>>> >>>> lists, >>>> >>>> but why doesn't this work? Am I misunderstanding something or is >>>> >>>> this a >>>> >>>> bug? >>>> >>>> >>>> >>>> Thanks, >>>> >>>> Luke >>>> >>>> ____________________ >>>> >>>> Racket Users list: >>>> >>>> http://lists.racket-lang.org/users >>>> >> >>>> >> >>>> >> >>>> >> ____________________ >>>> >> Racket Users list: >>>> >> http://lists.racket-lang.org/users >>>> >> >>>> > ____________________ >>>> > Racket Users list: >>>> > http://lists.racket-lang.org/users >>>> >>>> >>>> ____________________ >>>> Racket Users list: >>>> http://lists.racket-lang.org/users >>> >>> >>> >>> ____________________ >>> Racket Users list: >>> http://lists.racket-lang.org/users >>> >> >> >> ____________________ >> Racket Users list: >> http://lists.racket-lang.org/users >> > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
