Yes, it's the classic diamond dependency graph.
A
/ \
B C
\ /
D

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 something like.
A
/ \
B C
/ \
D D'

I may not write any code that uses the MarketModel (D) directly on the Trader (A).
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!

Cheers,

Dimitri

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.

then…

Cabal sets the paths for "import"ed
modules in the "hs-source-dirs:" and that is global to the whole
package.

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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