In my package's `gen/` folder

main.go

package main

import (
	"fmt"
	"strings"

	_ "github.com/abourget/featurette/design"

	"github.com/goadesign/goa/design"
	"github.com/goadesign/goa/dslengine"
	"github.com/goadesign/goa/goagen/gen_app"
	"github.com/goadesign/goa/goagen/gen_swagger"
)

// Call with: "go run gen/main.go" from project root

func main() {
	dslengine.FailOnError(dslengine.Errors)
	dslengine.FailOnError(dslengine.Run())

	apidesign := dslengine.Roots[0].(*design.APIDefinition)

	genapp.TargetPackage = "app"
	failOrPrint(new(genapp.Generator).Generate(apidesign))

	failOrPrint(new(genswagger.Generator).Generate(apidesign))
	
	// run custom generators...
}

func failOrPrint(files []string, err error) {
	dslengine.FailOnError(err)
	fmt.Println(strings.Join(files, "\n"))
}

Alternatively, the "make([]interface{}..." could be done by the Generator, if it so requires.. if the interface of dslengine should always be a []interface{} .. then I'd have a func in the dslengine to do that.. instead of here.