[plt-scheme] Contract Comments / Suggestions / Requests

I haven't been brave enough to try it on functions with contracts yet.
There is also the issue that these functions can suspend their execution -
for example to simulate time passing while work is going on.  In that case,
a continuation is put on the event list and later executed, resuming the
delayed function call.  I assume contracts (particularly the result
checking) will not be broken by this.

Doug

> -----Original Message-----
> From: Matthias Felleisen 
> Sent: Tuesday, October 19, 2004 2:01 PM
> To: Williams, M. Douglas
> Cc: Robby Findler
> Subject: Re: [plt-scheme] Contract Comments / Suggestions / Requests
> 
> This is a neat example. Thanks for brining it up. I hadn't considered
> gluing together "schedules" via macros and thus gluing together
> "suspended"
> contracts.
> 
> Robby -- this is another, but unforeseen "higher-order" effect,
> but with the twist that it's really first-order and checkable.
> 
> -- Matthias
> 
> 
> On Oct 19, 2004, at 3:43 PM, Williams, M. Douglas wrote:
> 
> > As an example for #4:
> >
> > In the simulation collection there is a macro, schedule, that schedules
> > events (for this discussion they can be function calls).  For example:
> >
> >   (schedule 100.0 (my-function 1 'b c))
> >
> > would schedule the function, my-function, to be applied to the
> > arguments (1
> > b <the value of c>) at (simulated) time 100.0.  If my-function has a
> > contract on it, it wouldn't be checked until the call is actually made
> > (at
> > simulated time 100.0) - and it would be from inside the main simulation
> > loop, not the user's invocation of the schedule macro.
> >
> > Currently, I use procedure-arity-includes? as a sanity check before I
> > add
> > the event to the event list, but it might still violate the contract
> > when it
> > is actually applied.
> >
> > I would like to be able to do the contract check (at least on the input
> > parameters - there is no result at that point to check) before I add
> > the
> > event to the event list and give an error at the point of the schedule
> > invocation.
> >
> > Doug
> >
> >> -----Original Message-----
> >> From: plt-scheme-admin at web-ext.cs.brown.edu
> >> [mailto:plt-scheme-admin at web-
> >> ext.cs.brown.edu] On Behalf Of Matthias Felleisen
> >> Sent: Tuesday, October 19, 2004 1:23 PM
> >> To: Williams, M. Douglas
> >> Cc: plt-scheme at web-ext.cs.brown.edu
> >> Subject: Re: [plt-scheme] Contract Comments / Suggestions / Requests
> >>
> >>   For list-related administrative tasks:
> >>   http://list.cs.brown.edu/mailman/listinfo/plt-scheme
> >>
> >>
> >> On Oct 19, 2004, at 11:50 AM, Williams, M. Douglas wrote:
> >>
> >>> I have a couple (of rather trivial) comments / suggestions / requests
> >>> (however anyone wants to interpret them) for contracts.  In general,
> >>> these are nitpicks that I can (and do) implement on my own (except
> >>> for
> >>> #4).  But I think they might useful enough to include in the
> >>> contracts
> >>> module - or at least it keeps me from including my own
> >>> contracts-extension module.
> >>>
> >>> 1) There are places in the language that require exact integers
> >>> (e.g.,
> >>> pretty much anyplace an index into something is needed).  How about
> >>> exact counterparts to the contracts that match integers.  For
> >>> example,
> >>> (exact-integer-in 1 10) or exact-natural-number?.  [Also add
> >>> exact-integer? as a counterpart to integer?.]
> >>
> >> Wonderful idea. I have used this, too.
> >>
> >>> 2) This is a total nitpick.  I would have rather seen natural-number?
> >>> named natural? (or natural-integer?).  I think the -number appended
> >>> makes it look to someone new to the language that it is higher in the
> >>> numeric hierarchy than it really is.  Plus, the exact-natural-number?
> >>> in #1 is getting a bit long.
> >>
> >> Robby is in the process of renaming these contracts. Great! Short is
> >> good here.
> >>
> >>> 3) At first I thought that in addition to natural-number? it would be
> >>> nice to have something matching positive integers, etc.  But I've
> >>> gotten so used to writing (integer-in 1 +inf.0) that it seems natural
> >>> (no pun intended).  Indeed, maybe natural-number? is superfluous.
> >>> Should we just encourage this format?
> >>>
> >>>
> >>> 4) This one may not be so trivial.  Is there any way to dynamically
> >>> check a list that could potentially be used as a function call (or
> >>> alternatively, a function and list of arguments to be applied)
> >>> against
> >>> a contract, prior to evaluation (or application) of the function?  (I
> >>> am thinking a super-extension of procedure-arity-includes? that one
> >>> could use to check against a contract instead of just the arity of
> >>> the
> >>> procedure.)
> >>
> >> Can you make an example? Sounds interesting.
> >>
> >> Thanks -- Matthias
> >>
> >>
> >>>
> >>>
> >>>
> >>> Doug