bug in language definition (strictness)

[Dan Weston]

 >      foldl (+) 0 [1..10000000] :: Integer
 >      *** Exception: stack overflow
 >      foldl' (+) 0 [1..10000000] :: Integer
 >      50000005000000

I thought both of these were perfectly well defined in denotational 
semantics (and equal to 50000005000000). The first is merely a failure 
of one person's computer to implement the (perfectly well-defined) 
denotational semantics of the program.

If we are going to document the officially valid deficiencies of each 
compiler and machine architecture, perhaps that should not be in the 
*language* definition, but in the Haskell Platform users' guide.

And those who are trying to distinguish between terminating and 
nonterminating bottom are claiming to solve the Halting Problem. There 
is no general way to reliably distinguish these two, and I believe that 
valid program transformations exist that can convert one to the other. 
Bottom has only one value, not two. Otherwise bottom would have been 
called buttocks.

Dan

Malcolm Wallace wrote:
>>> Yet I think it would be
>>> valid to say that seq can turn a non-terminating (exceptioning)  
>>> program
>>> into a terminating one.
>> Do you have an example of that?
> 
> Sure.
>      foldl (+) 0 [1..10000000] :: Integer
>      *** Exception: stack overflow
>      foldl' (+) 0 [1..10000000] :: Integer
>      50000005000000
> 
> The only difference between foldl and foldl' is strictness (the use of  
> seq).  By "non-terminating (exceptioning)" I of course really meant  
> "terminating with bottom" as opposed to "terminating with a defined  
> value", but since non-termination and exceptions are semantically both  
> bottom, you won't mind that slip.  :-)
> 
> Regards,
>      Malcolm
> 
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