Re: [Haskell-cafe] Python is lazier than Haskell

Dan, I believe there was some work on this functionality for GHC some time ago (agda-like goals for GHC, where ? in agda merely becomes 'undefined' in haskell.) See: https://github.com/sebastiaanvisser/ghc-goals This work was done a few years ago during a hackathon (the 09 Utrecht hackathon.) There is a frontend-executable providing goal information, as well as a patch to GHC to support it. It was never integrated into GHC and was left dead in the water essentially (for exactly what reasons, I do not know.) I find myself using the 'undefined' trick somewhat often as well. I'm not very familiar with agda, but familiar enough to have seen goals before in the interactive emacs mode, and I think this would be a nice feature for people who find themselves doing similar things. On Thu, Apr 28, 2011 at 3:18 PM, Dan Doel wrote:

(Sorry if you get this twice, Ertugrul; and if I reply to top. I'm stuck with the gmail interface and I'm not used to it.)

On Thu, Apr 28, 2011 at 11:27 AM, Ertugrul Soeylemez wrote:

...

I don't see any problem with this.  Although I usually have a bottom-up approach, so I don't do this too often, it doesn't hurt, when I have to.

I do. It's low tech and inconvenient.

Whenever I program in Haskell, I miss Agda's editing features, where I can write:

   foo : Signature    foo x y z = ?

Then compile the file. The ? stands in for a term of any type, and becomes a 'hole' in my code. The editing environment will then tell me what type of term I have to fill into the hole, and give me information on what is available in the scope. Then I can write:

   foo x y z = { partialImpl ? ? }

and execute another command. The compiler will make sure that 'partialImpl ? ?' has the right type to fill in the hole (with ?s again standing in for terms of arbitrary type). If the type checking goes through, it expands into:

   foo x y z = partialImpl { } { }

and the process repeats until my function is completely written. And of course, let's not forget the command for automatically going from:

   foo x y z = { x }

to

   foo Con1 y z = { }    foo Con2 y z = { }    foo Con3 y z = { }    ...

I don't think there's anything particularly Agda-specific to the above. In fact, the inference required should be easier with Haskell/GHC. Features like this would be pretty killer to have for Haskell development; then I wouldn't have to prototype in Agda. :)

-- Dan

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-- Regards, Austin