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.ma1...@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 >
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