QBS -> custom toolchain

[strahlex]

How can one add a custom build toolchain to QBS? As far as I understand this should be possible using a Module. I tried it like this:
@import qbs 1.0
import qbs.File
import qbs.FileInfo
import qbs.ModUtils

Module {
name: "hal"

FileTagger {
           patterns: ["*.hal"]
           fileTags: ["hal"]
       }

Rule {
    id: compiler
    inputs: ['hal']
    prepare: {
        var args = [];
        args.push(input.fileName);
        var cmd = new Command("echo", args);
        cmd.description = 'compiling ' + FileInfo.fileName(input.fileName);
        cmd.highlight = 'compiler';
        return cmd;
    }
}

}
@

@import qbs

Product {
name: "testProduct"
files: ["test.hal", "main.cpp"]

Group {
    name: "QML files"
    files: ["main.qml"]
    fileTags: ["qml"]
}

Depends { name: "hal" }

FileTagger {
          patterns: "*.qml"
          fileTags: ["qml"]
      }

Group {     // Properties for qml files
    name: "Install"
    fileTagsFilter: ["hal"]
    qbs.install: true
    qbs.installDir: "/blu/bin"
}

qbsSearchPaths: "machinekit"

}
@

Shouldn't this echo all my *.hal files?

Where can I get more help to QBS in general? The stuff in the documentation is not much at all.

Regards
Alexander