[Haskell-cafe] lazily updating dependencies, git submodules and cabal
defigueiredo at ucdavis.edu
Thu Sep 10 18:26:55 UTC 2015
Yes, it's the classic diamond dependency graph.
A = Trader, B = ProfitCalculator, C = Persistence, D = MarketModel.
It is not that I *want* Trader (A) to depend on two different versions
of MarketModel (D), that is just a consequence. I don't have a choice.
What I want is for the ProfitCalculator (B) and Persistence (C) to
always build. And if an update changes the MarketModel (D) from
underneath them, they might break. So, I want them to each lock-in a
specific version. In effect, I am forcing the graph above to turn into
I may not write any code that uses the MarketModel (D) directly on the
I do understand that there are at least 1 point to keep in mind:
types defined in D will be different from those in D' (typeclasses
will be defined twice)
But the benefit of *not* having to always keep everything building on
the latest version every time I update the MarketModel (D) is huge for me!
Em 10/09/15 06:50, timmy tofu escreveu:
> Using the 'cabal sandbox add-source' solution now requires that I
> "add-source" the MarketModel package too. Otherwise, any change I make
> to this package will not be tracked.
> Cabal sets the paths for "import"ed
> modules in the "hs-source-dirs:" and that is global to the whole
> I can't tell if you do or do not want ProfitCalculator and
> Persistence to track changes made in MarketModel.
> If you do, and both should be in lock-step with it (unlike your
> situation with Tax), then you don't have a problem.
> If not, then the problem is Trader would depend on ProfitCalculator
> which might depend on a different version of MarketModel than
> Persistence (upon which Trader also depends). That is a classic
> dependency problem and not a function of submodules or add-sourcing,
> per se. The Trader module seems to be at the top of this heap - why
> would you want the Trader to (indirectly) use one version of
> MarketModel through ProfitCalculator, and another through Persistence?
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