Module collisions in multi-dar projects

Questions
2

If a third project imports both of the dars you generate

dependencies
  - daml-finance-interface-0.0.1.dar
  - daml-finance-implementation-0.0.1.dar

and then from a new module you try to import one of the modules defined in both of these, you will get an error

  Ambiguous module name ‘Daml.Finance.Types’:
  it was found in multiple packages:
  daml-finance-interface-1.0.0 daml-finance-implementation-1.0.0

You can get around that one with package-qualified imports,

import qualified "daml-finance-interface" Daml.Finance.Types as Interface.Types
import qualified "daml-finance-implementation" Daml.Finance.Types as Implementation.Types

but then the types themselves wouldn’t match

foos = [Interface.Types.Foo, Implementation.Types.Foo]

  • Couldn't match expected type ‘Implementation.Types.Foo’
  with actual type ‘Interface.Types.Foo’
  NB: ‘Interface.Types.Foo’
  is defined in ‘Daml.Finance.Types’ in package ‘daml-finance-interface-1.0.0’
  ‘Implementation.Types.Foo’
  is defined in ‘Daml.Finance.Types’ in package ‘daml-finance-implementation-1.0.0’
  • In the expression: Interface.Types.Foo
  In the expression: [Implementation.Types.Foo, Interface.Types.Foo]
  In an equation for ‘foos’: foos = [Implementation.Types.Foo, Interface.Types.Foo]

So, my suggestion would be to split off the shared parts into a separate package that can be depended on by both interface and implementation packages. I think in that case these two wouldn’t need the .. parent directory in their configuration files, since they would just depend on the types package directly. The main drawback would be needing to build the dars sequentially, but that can be taken care of outside of damlc.

1 Like