<div dir="ltr">Could Andrew Myer's work on masked types (to eliminate nulls for object initialization) be relevant?<div><a href="http://www.cs.cornell.edu/Projects/jmask/">http://www.cs.cornell.edu/Projects/jmask/</a> </div></div><div class="gmail_extra"> <div class="gmail_quote">On Mon, Sep 29, 2014 at 3:30 PM, Matthias Felleisen <<a href="mailto:matthias@ccs.neu.edu" target="_blank">matthias@ccs.neu.edu</a>> wrote: <blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"> I guess the real problem is to create suitable default values so that the pass the type checker or to figure out a cast that forces TR to accept some other value as the default value (and making sure you never use the object). Undefined not completely solved. Argh. -- Matthias <div class="HOEnZb"><div class="h5"> On Sep 29, 2014, at 12:52 PM, Sam Tobin-Hochstadt <<a href="mailto:samth@cs.indiana.edu">samth@cs.indiana.edu</a>> wrote: > Ah, if you want to create truly cyclic structure with no base case > like this, then you'll have to do more work. Either you'll need to > expand the type of the `x` field in `foo` to allow an initial value, > or you'll need to create a dummy `foo` with that extended type, and > then copy the cyclic data once you've created it to a new version of > `foo`, using hash tables to track cycles. That's basically how > `shared` works, although I haven't tried implementing it in TR and it > might not be possible. > > Sam > > On Mon, Sep 29, 2014 at 12:33 PM, Konrad Hinsen > <<a href="mailto:konrad.hinsen@fastmail.net">konrad.hinsen@fastmail.net</a>> wrote: >> Sam Tobin-Hochstadt writes: >> >>> I recommend doing the mutation yourself, and not using `shared`. >>> That's the most obvious solution. >> >> Not for me, unfortunately, but probably I am missing something >> obvious. >> >> Here's explicit mutation in untyped Racket: >> >> #lang racket >> >> (struct foo (x) #:mutable) >> (struct bar (x)) >> >> (define f (foo (void))) >> (define b (bar f)) >> (set-foo-x! f b) >> >> (eq? (bar-x b) f) >> (eq? (foo-x f) b) >> >> That works fine. Moving to Typed Racket, this is rejected by the type >> checker because (void) is of type Void. Since I need a bar to make a >> foo and a foo to make a bar, I don't see how I can ever initialize my >> foo structure. >> >>> The reason that your `require/typed` doesn't work is that it creates >>> new versions of the placeholder functions, but those aren't the ones >>> that `shared` uses internally, so Typed Racket doesn't use the types >>> you've given. >> >> That makes sense, thanks for the explanation! >> >> Konrad. > ____________________ > Racket Users list: > <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> ____________________ Racket Users list: <a href="http://lists.racket-lang.org/users" target="_blank">http://lists.racket-lang.org/users</a> </div></div></blockquote></div> </div>