Depsolver is a dependency solver package for erlang. You supply it with a list of versioned objects that are in the world and then you can solve for different version constraints.

If no solution can be found, detailed back tracking information is returned that can be used to detect what exact dependencies are causing the problem.

1. In order to build you need rebar (https://github.com/basho/rebar)

2. run make

Lets say our world looks as follows

app1 that has versions "0.1"
  depends on app3 any version greater then "0.2"
 "0.2" with no dependencies
 "0.3" with no dependencies

app2 that has versions "0.1" with no dependencies
 "0.2" that depends on app3 exactly "0.3"
 "0.3" with no dependencies

app3 that has versions
 "0.1", "0.2" and "0.3" all with no dependencies

We can add this world to the system all at once as follows

Graph0 = depsolver:new_graph(),
Graph1 = depsolver:add_packages(
       [{app1, [{"0.1", [{app3, "0.2", '>='}]},
                {"0.2", []},
                {"0.3", []}]},
        {app2, [{"0.1", []},
                {"0.2",[{app3, "0.3"}]},
                {"0.3", []}]},
        {app3, [{"0.1", []},
                {"0.2", []},
                {"0.3", []}]}]).

We can also build it up incrementally using the other add_package and add_package_version functions.

Finally, once we have built up the graph we can ask depsolver to solve the dependency constraints. That is to give us a list of valid dependencies by using the solve function. Lets say we want the app3 version "0.3" and all of its resolved dependencies. We could call solve as follows.

depsolver:solve(Graph1, [{app3, "0.3"}]).

That will give us the completely resolved dependencies including app3 itself. Lets be a little more flexible. Lets ask for a graph that is rooted in anything greater then or equal to app3 "0.3". We could do that by

depsolver:solve(Graph1, [{app3, "0.3", '>='}]).

Of course, you can specify any number of goals at the top level.

• Author:: Eric Merritt ([email protected])
• Author:: James Casey ([email protected])

Copyright 2012 Opscode, Inc. All Rights Reserved.

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http://www.apache.org/licenses/LICENSE-2.0

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