This has a non-chaperone contract being used in a struct/c, I think? (FST (LST 1 2 3)) => struct/dc: expected chaperone contracts, but field a has #<barrier-contract>
Robby On Sun, Jan 6, 2013 at 2:40 PM, Sam Tobin-Hochstadt <sa...@ccs.neu.edu>wrote: > On Sun, Jan 6, 2013 at 3:23 PM, Robby Findler > <ro...@eecs.northwestern.edu> wrote: > > On Sun, Jan 6, 2013 at 2:18 PM, Sam Tobin-Hochstadt <sa...@ccs.neu.edu> > > wrote: > >> > >> > 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. > > > > > > I don't see why you can't tag them when something at a boundary and then > > check that something at another boundary instead of doing some deep > check. > > The problem is that I don't know what to tag them *with*. > > Consider the following program: > > #lang racket > > (struct kons (a d)) > (struct mt ()) > (define MT (mt)) > (define (FST v) > (when (eq? MT v) (error 'empty)) > (kons-a v)) > (define (RST v) > (when (eq? MT v) (error 'empty)) > (kons-d v)) > (define (LST . x) > (if (empty? x) > MT > (kons (first x) (apply LST (rest x))))) > (define (LST/C elem/c) > (define C (recursive-contract > (or/c (λ (v) (eq? v MT)) > (struct/c kons elem/c C)))) > C) > (provide/contract > [LST (parametric->/c (A) (->* () #:rest A (LST/C A)))] > [FST (parametric->/c (A) (-> (LST/C A) A))] > [RST (parametric->/c (A) (-> (LST/C A) (LST/C A)))]) > > This is the essence of Neil's polymorphic list program, as implemented > by Typed Racket. I don't know how to change those contracts to not be > really expensive, because I can't pick the instantiation of A at > runtime to tag the structure instances with. > > Sam >
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