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

[Gregory Crosswhite]

On Dec 22, 2011, at 12:40 PM, Alexander Solla wrote:

> 
> 	fst _|_ = _|_
> 
> This expression is basically non-sense.

This is only "nonsense" because you refuse to accept that there are valid formalisms other than your own that contain _|_ as a perfectly valid entity.  :-)


> Should we accept straight-forwardly ill-typed expressions like:
> 
>     data Strict a = Strict !a
>     fst (Strict [1..])
> 
> just because the argument is "strictly" a bottom? Bottom inhabits every type, but only vacuously.

No, each type has its own value for _|_, and your example demonstrates why this makes more sense than making all _|_'s be equivalent.


> Things like seq, unsafeCoerce, and the like, are defined as (functions into) bottom in GHC.Prim, and the real semantic-changing magic they perform is done behind the scenes.  It cannot be expressed as Haskell in the same Haskell context it is used.  So assuming you mean something like:
> 
>    fst (seq [1..] (1,2))
> 
> I must respond that you are using one of these magical keywords which change Haskell's semantics.  They should be avoided.

So... now you want to throw out seq so that we no longer have a way to force the evaluation of values, and the motivation for this is because when we throw out _|_ then we no longer have a formal way to describe the semantics of seq?


> Refusing to use bottom in our semantics doesn't make life better by forcing us to stay within a total fragment of the language, it actually makes life harder by removing from us a useful tool for knowing *how* to stay within a total fragment of the language.
> 
> I am collapsing the semantics for "distinct" bottoms into a single bottom and noting that it has no interpretation as a Haskell value.

I agree that if you collapse all of the distinct bottoms then you get a mess, but since whenever we are talking about semantics in the Haskell community we give each type has its own _|_ it is an incredibly moot point;  it's like saying that the problem with cars is that if you remove all of their wheels then they have a lot of trouble getting anywhere at all.  :-)

Cheers,
Greg
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