[Haskell-cafe] If you'd design a Haskell-like language, what would you do different?

[Heinrich Apfelmus]

Alexander Solla wrote:
>> And denotational semantics is not just nice. It is useful. It's the best
>> way to understand why the program we just wrote doesn't terminate.
> 
> Denotational semantics is unrealistic.  It is a Platonic model of
> constructive computation.  Alan Turing introduced the notion of an "oracle"
> to deal with what we are calling bottom.  An oracle is a "thing" that
> (magically) "knows" what a bottom value denotes, without having to wait for
> an infinite number of steps.  Does Haskell offer oracles?  If not, we
> should abandon the use of distinct bottoms.  The /defining/ feature of a
> bottom is that it doesn't have an interpretation.

Huh? I don't see the problem.

Introducing bottom as a value is a very practical way to assign a 
well-defined mathematical object to each expression that you can write 
down in Haskell. See

   http://en.wikibooks.org/wiki/Haskell/Denotational_semantics

It's irrelevant whether _|_ is "unrealistic", it's just a mathematical 
model anyway, and a very useful one at that. For instance, we can use it 
to reason about strictness, which gives us information about lazy 
evaluation and operational semantics.


Best regards,
Heinrich Apfelmus

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