[plt-scheme] define/contract/provide ?

Thanks Robby and Noel.

So if I understand correctly, define/contract would enforce calls to
the function even from inside the module: define/contract is
intra-module (function boundary) and provide/contract is inter-module
(module boundary).  Is that correct?

If so, the only practical difference I can see would be performance:
If say the module code trusts itself and doesn't want to pay the price
for runtime checking. Is that correct, or is there more nuance to
contracts that I'm not yet understanding?

Also in general are contracts a way to avoid littering functions with
explicit runtime checks like "(unless (some-type-predicate? arg)
(error))", but effectively are just that behind the scenes?

On Sun, Mar 21, 2010 at 2:29 PM, Greg Hendershott
<greghendershott at gmail.com> wrote:
> Thanks Robby and Noel.
>
> So if I understand correctly, define/contract would enforce calls to
> the function even from inside the module: define/contract is
> intra-module (function boundary) and provide/contract is inter-module
> (module boundary).  Is that correct?
>
> If so, the only practical difference I can see would be performance:
> If say the module code trusts itself and doesn't want to pay the price
> for runtime checking. Is that correct, or is there more nuance to
> contracts that I'm not yet understanding?
>
> Also in general are contracts a way to avoid littering functions with
> explicit runtime checks like "(unless (some-type-predicate? arg)
> (error))", but effectively are just that behind the scenes?
>
> On Sun, Mar 21, 2010 at 8:52 AM, Robby Findler
> <robby at eecs.northwestern.edu> wrote:
>> Matthew answered the macro issues, but there is a difference between
>> contracts and types that seems to be tripping you up. Specifically, a
>> contract always comes with a boundary. The contract governs how the
>> code inside the boundary interacts with the code outside. This is
>> unlike types that express facts about the program. For
>> provide/contract (for example), the boundary is the module; the
>> contracts govern the values that flow into and out of the module (via
>> the functions defined in the module).
>>
>> So, that's something to keep in mind when you are defining your macro:
>> where is the inside and where is the outside for your contracts?
>>
>> Robby
>>
>> On Sat, Mar 20, 2010 at 4:35 PM, Greg Hendershott
>> <greghendershott at gmail.com> wrote:
>>> Wrapping my brain around modules and contracts. Coming from C/C++/C# mindset.
>>>
>>> Have successfully used define and provide/contract in a module
>>>
>>> Just noticed define/contract. I'm thinking, hey, this is how my C-ish
>>> brain works. Define the function and its types/contract in one swell
>>> foop.
>>>
>>> Small annoyance is now I have to type provide by itself.
>>>
>>> So I'm wondering, why isn't there a define/contract/provide?  Isn't
>>> doing all three a common scenario when making a module?  Or am I
>>> carrying baggage from my C background?
>>>
>>>
>>> On a related note, I risked further brain burn by attempting to
>>> provide (sorry) this myself with define-syntax.
>>>
>>> Attempt 1 was this:
>>>
>>>  (define-syntax-rule (define/contract/provide (id args ...) (contract
>>> ...) body-expr ...)
>>>    (begin
>>>      (define/contract (id args ...) (contract ...) body-expr ...)
>>>      (provide id)))
>>>
>>> But doesn't work because provide doesn't work inside (begin). No error
>>> making the module, but user of it doesn't see the function since
>>> provide inside begin (I think?).
>>>
>>> Attempt 2 was this:
>>>
>>>  (define-syntax-rule (define/contract/provide (id args ...) (contract
>>> ...) body-expr ...)
>>>    (define/contract (id args ...) (contract ...) body-expr ...)
>>>    (provide id))
>>>
>>> But that complains:
>>>  define-syntax-rule: too many templates in: ((provide id))
>>>
>>>
>>> Thanks in advance for any help!
>>>
>>> Greg
>>> _________________________________________________
>>>  For list-related administrative tasks:
>>>  http://list.cs.brown.edu/mailman/listinfo/plt-scheme
>>>
>>
>