Dagger is a task scheduler and runner. In the best case it should help run complex workflows. Goals:

• no extra language to learn, no XML wiring of tasks
• autogenerated command line interface

Inspiration: luigi and other tools.

Work in progress:

$ go run example/example.go

What worked:

• Split Task interface into Runner, Outputter, Requirer.

• Easy to intergrate standalone files:

    type OutputFunc string
  
    func (f OutputFunc) Output() dagger.Target {
        return dagger.LocalTarget{Path: f.filename}
    }
  
    ...
  
    type SomeTask struct {}
  
    func (t SomeTask) Requires() dagger.TaskMap {
        return dagger.TaskMap{
            "x": OutputFunc("/path/to/file"),
        }
    }
  

What didn't work:

Within Run() we need access to the most concrete types, whereas in Requires() and Output() we would like to return some interface.

If we want to force the return value of Output() to fulfill an interface, we can write:

// Output fulfills the Outputter interface.
func (task BogusAggregation) Output() dagger.Target {
    return dagger.LocalTarget{Path: dagger.AutoPathExt(task, "tsv")}
}

But inside Run we want to Open, Write or Close. Alternative:

var _ dagger.Target = dagger.LocalTarget{}

But then, we cannot check for the interface to the task struct.

Example: http://play.golang.org/p/VeGcg4pc4y

Similar on the input side. Targets can be heterogeneous, files, database, etc.