Re: [Haskell-cafe] Backward compatibility

On Fri, 2013-05-03 at 10:40 -0700, Hilco Wijbenga wrote:

On 3 May 2013 09:44, Niklas Hambüchen wrote:

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While I certainly enjoy the discussion, how about addressing one of the original problems:

On 02/05/13 13:27, Adrian May wrote:

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I just tried to use Flippi. It broke because of the syntax change so I tried WASH. I couldn't even install it because of the syntax change.

I just fixed that in https://github.com/nh2/flippi (note that I have never seen this code before nor even known about it).

https://github.com/nh2/flippi/commit/5e2fa93f82b4123d0d5b486209c3b722c4c1313...

Had to delete 5 imports and convert one time value.

Took me around 3 minutes.

It seems fair to say that Haskell's designers lean more to evolution than maintaining backward compatibility. This reminds me of "Go" (the programming language). The approach chosen by Go's designers was to create a tool (gofix) that would automatically fix one's code to comply with the latest standard. See [http://talks.golang.org/2012/splash.article#TOC_17.] (yes, include that last period).

Given the apparent simplicity of the changes needed to keep one's Haskell code up to snuff and the strong typing inherent in Haskell code, would it not be possible to create something similar? If there is a tool that moves (most of) one's code from Haskell version n to n+1 then making breaking changes would be even less of an issue.

Just an idea, I have no clue about its feasibility...

I mentioned the same on #haskell today. Something like Coccinelle (http://coccinelle.lip6.fr) "semantic patches" could be really useful to automate (some) API & language changes. Somewhat like (but better than) the Python '2to3' tool. I think some message about a GSoC project regarding an AST-based refactoring tool was posted to this list. That might be a useful building block for such tool? Imagine one day whenever a new HP release is made, GitHub pull-requests are created automatically based on a automatically-generated patch verified through a compilation&test-cycle on TravisCI for GH-hosted packages published on Hackage. Nicolas