[ghc-steering-committee] Is @ a name-space override, or a visibility override?

[Simon Marlow]

I haven't followed this debate, but the main question I have is: what are
the implications of choosing one view over the other?

Cheers
SImon

On Fri, 13 Nov 2020 at 14:10, Spiwack, Arnaud <arnaud.spiwack at tweag.io>
wrote:

> Dear all,
>
> There is a debate which has been held in our heads for quite some time
> now. But we’ve never really had the conversation. This debate has been
> raised again in the context of proposal #281. But I’d rather make a
> separate thread about it.
>
> The question is the following:
>
> When I write
>
> f @t
>
> Am I using @ as a way to change an invisible argument into a visible
> argument? Or am I using @ to insert a type expression into a term
> expression?
> ------------------------------
>
> The truth is that it’s doing both at the same time. So some of us have
> taken to believing that the One True Meaning™ of @ is to override
> (in)visibility. While others have taken to believing that the One True
> Meaning™ of @ is to insert types in term.
>
> And, in both cases, we believe the other part to be incidental.
>
> In favour of types-in-term, there is the pretty-printer for Core, which,
> if I’m not mistaken, uses @t to denote type applications (and all type
> applications are visible in Core, so there is no visibility override to be
> had).
>
> Whatever we think about this, it appears that the fact that this meaning
> ascription is implicit has caused some anguish. So I think that we should
> have this discussion explicitly for once.
>
> I chose to do so in a different thread than the #281 discussion, because
> this discussion stands on its own.
>
> Anyway, the floor is yours.
>
> /Arnaud
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