Evaluating type expressions in GHCi

[Sean Leather]

Hi Simon,

On Fri, Sep 23, 2011 at 10:04, Simon Peyton-Jones wrote:

> I did this.  ****
>
> ** **
>
> *TF> :kind F Int****
>
> F Int :: *****
>
> *TF> :kind! F Int****
>
> F Int :: *****
>
>           = Bool****
>
> ** **
>
> In the end I just made an eager version of :kind as the command: in
> addition to displaying the kind of the type, it normalises it and shows the
> result.****
>
> ** **
>
> It’s in HEAD.  Documentation to come when I get home.
>

That's great! Much appreciated.

I’m not wedded to this command name.  If everyone wants “:normalise” it
> would only take a 1-line change.
>

I'm also not picky about the name. But I do think fewer keystrokes are
better. I guess with ":kind!" you have have to type at least ':', 'k', '\t',
and '!', whereas with a unique first character such as 'n', you only have to
type ':', 'n' [1]. But that's the only real "concern" I would have about the
name.

Safe travels!

Regards,
Sean

[1] This presupposes that people actually want to use such a command. It
does make working with type families easier. And, now that I think about it,
I needed something like that this several years ago.
http://splonderzoek.blogspot.com/2009/06/rfc-extensible-typed-scanf-and-printf.html
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