[Nix-dev] Haskell NG

[Peter Simons]

Hi Russel,

 >> 2) Haskell packages support 'deepOverride'.
 >
 > How would you feel about using my overrideScope functionality from my
 > haskellPackagesFixpoint branch instead?

the first version of my re-factored Haskell code defined deep overrides exactly
the way you did it. Check out the "definePackage" function in [1]. You'll find
that I studied your work thoroughly.

My impressions are:

 1. overrideScope and deepOverride achieve the same goal. I discovered no case
    where one function worked but the other one didn't.

 2. deepOverride is a standard function every callPackage derivation supports.
    overrideScope, on the other hand, is not.

 3. deepOverride is implemented in a simple generic algorithm (for appropriate
    definitions of the term "simple") that requires no special support from the
    haskellPackages record to function. overrideScope, on the other hand, needs
    the magic nixClass attribute (__unfix__ in my code) to build a stack of
    extension functions.

Ultimately, I felt that I should stick to the standard deepOverride mechanism
mostly due to Occam's razor'ish reasoning: I'd rather not introduce a new
sophisticated tying-the-knot mechanism to haskellPackages just to do the same
thing that deepOverride can do already.

Does that make sense?

Best regards,
Peter


[1] https://github.com/NixOS/cabal2nix/blob/070a5342a9dd5bbb6387f16750941881889c4cc8/doc/ng.nix