double2.yaml

name: double2
doc: |-
  A machine that double numbers and protests requests for doubling non-numbers.
patternsyntax: json
nodes:
  start:
    branching:
      branches:
      - target: listen
  listen:
    branching:
      type: message
      branches:
      - pattern: |
          {"double":"?x"}
        guard:
          interpreter: ecmascript
          source: |-
            var bs = _.bindings;
            var f = parseFloat(bs["?x"]);
            if (isNaN(f)) {
               return null;
            } else {
               bs["?x"] = f; // Overwrite with the number.
               return bs;
            }
        target: double
      - pattern: |
          {"double": "?x"}
        target: complain
  double:
    action:
      interpreter: ecmascript
      source: |-
        _.out({doubled: _.bindings["?x"]*2});
        return _.bindings;
    branching:
      branches:
        - target: cleanup
  complain:
    action:
      interpreter: ecmascript
      source: |-
        _.out({bad: _.bindings["?x"]});
        return _.bindings;
    branching:
      branches:
        - target: cleanup
  cleanup:
    action:
      interpreter: ecmascript
      source: |-
        delete _.bindings["?x"];
        return _.bindings;
    branching:
      branches:
        - target: listen