Test cases and static typing

[Pascal Costanza]

Dirk Thierbach wrote:
> Pascal Costanza <costanza at web.de> wrote:
> 
>>Dirk Thierbach wrote:
> 
>>OK, I have got it. No, that's not what I want. What I want is:
>>
>>testxyz obj = (concretemethod obj == 42)
>>
>>Does the code compile as long as concretemethod doesn't exist?
> 
> No. Does your test pass as long as conretemthod doesn't exist? It doesn't,
> for the same reason.

As long as I am writing only tests, I don't care. When I am in the mood 
of writing tests, I want to write as many tests as possible, without 
having to think about whether my code is acceptable for the static type 
checker or not.

>>>It's the same with compile-time type errors. The only difference is
>>>that they happen at compile-time, not at test-suite run-time, but the
>>>necessary reaction is the same: Fix your code so that all tests (or
>>>the compiler-generated type "tests") pass. Then continue with the next
>>>step. 
> 
>>The type system might test too many cases.
> 
> I have never experienced that, because every expression that is valid
> code will have a proper type.
> 
> Can you think of an example (not in C++ or Java etc.) where the type
> system may check too many cases?

Here is one:

(defun f (x)
   (unless (< x 200)
     (cerror "Type another number"
             "You have typed a wrong number")
     (f (read)))
   (* x 2))

Look up 
http://www.lispworks.com/reference/HyperSpec/Body/f_cerror.htm#cerror 
before complaining.



Pascal

-- 
Pascal Costanza               University of Bonn
mailto:costanza at web.de        Institute of Computer Science III
http://www.pascalcostanza.de  Römerstr. 164, D-53117 Bonn (Germany)