"Strong typing vs. strong testing"

Pascal J. Bourguignon pjb at informatimago.com
Fri Oct 1 19:36:18 CEST 2010


Seebs <usenet-nospam at seebs.net> writes:

> On 2010-10-01, Pascal J. Bourguignon <pjb at informatimago.com> wrote:
>> Seebs <usenet-nospam at seebs.net> writes:
>>> On 2010-10-01, Pascal J. Bourguignon <pjb at informatimago.com> wrote:
>>>> compiler passes wrong type      wrong result        fails at run-time
>>>>                                 (the programmer     (with exception
>>>>                                 spends hours        explaining this is
>>>>                                 finding the         the wrong type)
>>>>                                 problem)
>>
>>> I have no clue what exact scenario you're talking about here.  I've never
>>> seen a bug that could plausibly be described as "compiler passes wrong
>>> type" which wasn't picked up quickly by running with more warnings enabled.
>
>> This is the scenario discussed in this thread, a long is passed to
>> maximum without a compiler warning.
>
> The compiler didn't pass the wrong type, the user did.

And the compiler passed it on without saying anything.

>>> And on the other end of things, it is not always obvious or straightforward
>>> to figure out *why* the dynamic language has ended up with something of the
>>> wrong type, or what's wrong with that type.
>
>> It is on the contrary rather obvious or easily discoverable, looking at
>> the backtrace, and inspecting the data structures referenced from it.
>
> This is a fascinating assertion, but it is slightly marred by not actually
> being generally true.  It's often the case that it's pretty obvious, but
> sometimes it's not so obvious -- it can take quite a bit of doing to figure
> out how or where some hunk of a data structure got set up wrong.  It's very
> easy to find the call where a nil was passed to something expecting some kind
> of integer; it's sometimes not so easy to find the completely unrelated hunk
> of code which modified the data structure half an hour earlier.

When debugging C program, you are perfectly right.  
But I don't observe the same when debugging lisp programs. 


-- 
__Pascal Bourguignon__                     http://www.informatimago.com/



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