[racket] [Typed Racket] define-predicate for union with functions

(And this is not a limitation of Typed Racket but a fundamental problem of CS.) 


On May 20, 2013, at 11:07 AM, Eric Dobson <eric.n.dobson at gmail.com> wrote:

> No, you cannot define predicates for function types. If you explain
> the problem you have, we might be able to explain another solution
> that will work.
> 
> On Mon, May 20, 2013 at 1:32 AM, Paul Leger <pleger at gmail.com> wrote:
>> Hi all,
>>      Maybe, this question is very easy. In the following code, I try
>> defining a predicate for T2, but I cannot because T1 it is a function.
>> 
>> (define-type T1 (Symbol -> Any) )
>> (define-type T2 (U Symbol Number T1))
>> 
>> ;(define-predicate T1? Procedure) ;this line is useless
>> 
>> (define-predicate T2? T2)
>> 
>>> Type Checker: Type T2 could not be converted to a contract. in: T2
>> 
>> My unsuccessful answer is:
>>  (define-type T2 (U Symbol Number Procedure))
>> 
>> I do not like it because I lose the relationship between T1 and T2. Are
>> there some possibility
>> 
>> Thank in advance,
>> Paul
>> 
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