[racket-dev] Please help me to understand the two lines.

The results of functions are all given by contracts. So, this is saying that
the function named "boolean?" returns something that, when passed to
"boolean?", returns #true.

This is a confusing example to start with, tho, if you had number?, you'd
see:

  (number? v) -> boolean?
  v : any/c

which is saying that the function named "number?" returns something that,
when passed to "boolean?" returns #true.

As for the any/c vs any: they are two separate things. "any/c" is general
purpose contract that allows anything. "any" is special syntax that is only
allowed inside function contracts. You can think of "any" as a more
restricted form of "any/c" and that's 95% of the story.

Also, do check out this section for more on contracts:

  http://docs.racket-lang.org/guide/contracts.html

Robby

On Mon, May 30, 2011 at 9:07 AM, Yingjian Ma <yingjian.ma1955 at gmail.com>wrote:

>   The lines are from
> http://pre.racket-lang.org/docs/html/reference/booleans.html
> section 3.1
>
> The lines are:
> (boolean?<http://pre.racket-lang.org/docs/html/reference/booleans.html#%28def._%28%28quote._%7E23%7E25kernel%29._boolean%7E3f%29%29>
>  v) → boolean?<http://pre.racket-lang.org/docs/html/reference/booleans.html#%28def._%28%28quote._%7E23%7E25kernel%29._boolean%7E3f%29%29>
>     v : any/c<http://pre.racket-lang.org/docs/html/reference/Data-structure_Contracts.html#%28def._%28%28lib._racket/contract/private/misc..rkt%29._any/c%29%29>
>
> Question 1
> The result (boolean?<http://pre.racket-lang.org/docs/html/reference/booleans.html#%28def._%28%28quote._%7E23%7E25kernel%29._boolean%7E3f%29%29>
>  v) is a boolean.  Why is it not
>   (boolean?<http://pre.racket-lang.org/docs/html/reference/booleans.html#%28def._%28%28quote._%7E23%7E25kernel%29._boolean%7E3f%29%29>
>  v) → boolean  instead of  (boolean?<http://pre.racket-lang.org/docs/html/reference/booleans.html#%28def._%28%28quote._%7E23%7E25kernel%29._boolean%7E3f%29%29>
>  v) → boolean?<http://pre.racket-lang.org/docs/html/reference/booleans.html#%28def._%28%28quote._%7E23%7E25kernel%29._boolean%7E3f%29%29>
> ?
>
>  Question 2
> If v can be anything,  why not just use any instead of using any/c<http://pre.racket-lang.org/docs/html/reference/Data-structure_Contracts.html#%28def._%28%28lib._racket/contract/private/misc..rkt%29._any/c%29%29>
> ?
>
>  Question 3
> What does / and c mean?
>
> BTW, did I missed the definition of / and c?  I have not read the entire
> document.
>
> Thanks a lot.
>
> _________________________________________________
>  For list-related administrative tasks:
>  http://lists.racket-lang.org/listinfo/dev
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.racket-lang.org/dev/archive/attachments/20110530/fb9e6db2/attachment.html>