On Sun, Jan 6, 2013 at 3:13 PM, Robby Findler <ro...@eecs.northwestern.edu> wrote: > I wouldn't say you'd do it for cons cells (they are special in the runtime). > This is for structs that are declared in TR. You would add the field > everywhere (or places where the programmer asks only).
Right, I know how the real Racket `cons` is implemented, that's just a simple example. Imagine if `cons` was a TR data structure. > The boundaries have the information; that's how the contracts got inserted > in the first place. No, the contracts are parametric contracts using `parametric->/c`, and thus don't have any information about the types used at all. Sam > > Robby > > > On Sun, Jan 6, 2013 at 2:03 PM, Sam Tobin-Hochstadt <sa...@ccs.neu.edu> > wrote: >> >> On Sun, Jan 6, 2013 at 2:55 PM, Robby Findler >> <ro...@eecs.northwestern.edu> wrote: >> > What if you added an extra field to immutable values (ie all TR structs >> > would have this hidden field) such that, when they passed across a >> > boundary, >> > the field got mutated to say what type it passed at. Then, when the >> > value >> > passed back into TR, TR could check to see if has this secret field and >> > what >> > the type was and then avoid more checking. >> >> The problem is that this info isn't available anywhere (and I'm not >> sure it's really sensible). Consider the `cons` function (on lists >> only). If you write `(cons 'hello empty)` in untyped code, what type >> should get inserted, and where should that be calculated? This >> calculation can't really be done both automatically and correctly >> ahead of time, and would add a bunch more expense. >> >> Sam > > _________________________ Racket Developers list: http://lists.racket-lang.org/dev
