Python is DOOMED! Again!

[Steven D'Aprano]

Paul Rubin wrote:

> Steven D'Aprano <steve+comp.lang.python at pearwood.info> writes:
>> Some degree of weakness in a type system is not necessarily bad. Even the
>> strongest of languages usually allow a few exceptions, such as numeric
>> coercions.
> 
> Haskell doesn't have automatic coercions of any sort.  You have to call
> a conversion function if you want to turn an Int into an Integer.

That's unusual but not unheard of.


>> I've never come across a language that has pointers which insists on
>> having a separate Nil pointer for ever pointer type
> 
> Haskell's idiomatic substitute for a null pointer is a Nothing value
> (like Python's None) and there's a separate one for every type.  The FFI
> offers actual pointers (Foreign.Ptr) and there is a separate nullPtr
> for every type.

Well, I live and learn.


>> the compiler will allow Nil to be used for any pointer type. Anything
>> else would be impractical.
> 
> It's completely practical: polymorphism and type inference get you the
> value you want with usually no effort on your part.

But it's the "usually" that bites you.

If I have an arbitrary pointer, and I want to check if it is safe to
dereference, how do I do it? Surely I'm not expected to write something
like:

if type(ptr) == A:
    if ptr != Anil: ...
if type(ptr) == B:
    if ptr != Bnil: ... 

etc. That would be insane. So how does Haskell do this?

 
>> What if you add two empty objects?
>> js> {} + {}
> 
> OMG, javascript is worse than I thought
> 
>> https://www.destroyallsoftware.com/talks/wat
> 
> Can't view, needs flash. :(

At the bottom of the page is a link to a .mov version. If you can't
play .mov files either, contact me off list.


> Try this instead (NFSW): https://www.youtube.com/watch?v=FJ7QsEytQq4



-- 
Steven