[Nix-dev] builderDefs, composedArgsAndFun

[Michael Raskin]

>Hi,
>
>there are some functions in nixpkgs that I always avoided to use and understand.
>A couple of them are builderDefs and composedArgsAndFun.
>I'm reading their implementation right now but they don't look straightforward to me.
>Can someone give me a hint on what they do or point me to some documentation?

builderDefs compose build process out of phases instead of running 
always the same functions, although some of executions of some of the
functions do nothing. 

It was written before there was any reasonable overriding in Nixpkgs to
provide overriding (sometimes changing preConfigure with overrides is
still hard). Also, it doesn't require additional tricks for passing $out
in configureFlags and it is possible to add a new archive format support
in trunk with out a rebuild (and overall it controls more of the build
choices on Nix-language level, instead of in the bash script).

>In particular, i would like to update the expression for the Io language which is now old (2008) which employ builderDefs.

If it is a complete rewrite because Io's build system is now 
rewritten upstream, there is no reason to care about my old 
expression.