On Thu, Sep 16, 2010 at 1:40 AM, Markku Rontu <markku.ro...@iki.fi> wrote: > Thanks for the info. > > On Thu, Sep 16, 2010 at 12:27 AM, Robby Findler > <ro...@eecs.northwestern.edu> wrote: >> >> Contracts are implemented by creating wrapper functions and >> define/contract does this by changing how the variable reference >> "unfun" works. It actually creates the wrapper function at the point >> of the variable reference and so is creating two in this case. > > My next question might have been how have you implemented contracts, i.e. > how do you attach contracts to procedures? In this case you definitely need > to wrap the procedure so that the contract gets called in the appropriate > places but I'm surprised it's done at the reference site and not in the > definition.
Since blame might be assigned to the use site, the wrapper has to come there. >> >> I expect that at some point define/contract may change in the future >> to create fewer wrappers; as you can probably guess in this case the >> wrappers are identical so we only need one. Probably this exact case >> won't change but others may. >> >> In general, when contracts are involved, you cannot rely on eq?-based >> identity for procedures. If you want some kind of identity on >> procedures, I recommend you use applicable structs. > > > What I'm trying to do is to attach certain metadata to procedures. So I need > a way to map from procedures to their metadata. Any ideas on how to > implement this? Am I really forced to wrap everything behind my own wrapper > that provides me a workable identity for each procedure? > > So there is no reliable way to refer to procedures and attach the metadata > but that I need to always custom-define and wrap them? This would mean there > is no reliable way to attach metadata to third party procedures that may or > may not be defined with define/contract? Or I have to make require to wrap > everything required too somehow? Then there is of course the question of > macros and attaching metadata to them... > > In general, it would be nice to have a standard way of attaching metadata to > any value. Or is this a silly idea? For procedures at least, you might look at structs-as-procedures. You can make a struct that contains a function in such a way that the struct actually acts as a function and uses the contained function when it is called, etc. http://docs.racket-lang.org/reference/procedures.html?q=prop:&q=struct#(def._((lib._racket/private/base..rkt)._prop~3aprocedure)) Robby _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
