DSL EXPRESSION:
for (k in $*) { emit { k : k } }


AST:
* statement block
    * single-variable for-loop "for"
        * local variable "k"
        * full record "$*"
        * statement block
            * emit statement "emit"
                * emittable list
                    * map literal "{}"
                        * map-literal key-value pair ":"
                            * local variable "k"
                            * local variable "k"
                * no-op
                * no-op

