[racket] Whats the difference between a predicate and a flat contract?

Are flat-contract and flat-contract-predicate equivalent?

> ((flat-contract 'x) 'x)
#t
> ((flat-contract-predicate 'x) 'x)
#t
> ((flat-contract 'x) 'y)
#f
> ((flat-contract-predicate 'x) 'y)
#f
>

Harry

On Tue, Dec 4, 2012 at 9:41 PM, Robby Findler
<robby at eecs.northwestern.edu> wrote:
> It does that for symbols, but not everything.
>
> This is the place you should be looking, I think.
>
> http://docs.racket-lang.org/reference/contracts.html
>
> Robby
>
> On Tue, Dec 4, 2012 at 8:38 PM, Harry Spier <vasishtha.spier at gmail.com> wrote:
>> OK I see the docs to flat-contract? but not flat-contract
>> http://docs.racket-lang.org/reference/contract-utilities.html#(def._((lib._racket/contract/private/misc..rkt)._flat-contract~3f))
>> mention that flat-contracts are more than predicates.  Those docs
>> don't mention it, but it appears from experimentation that
>> (flat-contract something) produces a procedure such that
>> ((flat-contract something) x) is #t if something eq? x .
>>
>> Harry Spier
>>
>> On Tue, Dec 4, 2012 at 8:57 PM, Robby Findler
>> <robby at eecs.northwestern.edu> wrote:
>>> On Tue, Dec 4, 2012 at 7:28 PM, Carl Eastlund <cce at ccs.neu.edu> wrote:
>>>> On Tue, Dec 4, 2012 at 7:49 PM, Robby Findler <robby at eecs.northwestern.edu>
>>>> wrote:
>>>>>
>>>>> Flat contracts includes more things than contracts. For example:
>>>>>
>>>>> [robby at yanpu] ~/git/plt/collects/scribblings/reference$ racket
>>>>> Welcome to Racket v5.3.1.9.
>>>>> > (flat-contract? 'x)
>>>>> #t
>>>>> > (procedure? 'x)
>>>>> #f
>>>>>
>>>>> The flat-contract function is a holdover from the days when flat contracts
>>>>> weren't able to be used directly as predicate functions.
>>>>>
>>>>>
>>>>> I'll push a clarification to the docs for flat-contract.
>>>>
>>>>
>>>> Isn't that the wrong way around?  The flat-contract function lets you use a
>>>> predicate as a contract, not a contract as a predicate.  Presumably it's
>>>> from before predicates could be used as contracts, although I hadn't
>>>> realized there was such a time.
>>>
>>> There was a time when you had to call 'flat-contract' to turn a
>>> predicate into a contract, yep. There was a housecleaning (anyone
>>> remember the days when there were multiple suffixes (not just "/c") on
>>> the combinators?) and I probably should have gotten rid of it at that
>>> time, but I didn't.
>>>
>>> (Oh and I mean "contracts" where I wrote "preducate functions" above. Oops.)
>>>
>>> Robby