Updating fields type with a default type

fields_update.json

{
    "description": "Script that updates the field types for an existing Source. The `base-type` is assigned to all the fields unless otherwise stated in `explicit-types`.\nThe `explicit-types` argument expects a list of [field, type] pairs like:\n\n[[\"field1\", \"categorical\"], [\"field2\", \"numeric\"]]",
    "inputs": [
        {
            "name": "source-id",
            "type": "source-id",
            "description": "Select the source to be updated"
        },
        {
            "name": "base-type",
            "type": "string",
            "description": "Type that will be assigned to fields if not specified in explicit-types",
            "default": "numeric"
        },
        {
            "name": "explicit-types",
            "type": "list",
            "description": "List of [field, type] pairs when different from base type (e.g.:[[\"field\", \"categorical\"], [\"field2\", \"numeric\"]])",
            "default": []
        }
    ]
}

fields_update.whizzml

;; Auxiliar function to get the field ID
;; corresponding to each explicitly typed field
(define (get-field-id fields field-name)
  (let (field-ids (keys fields))
    (loop (field-ids field-ids)
      (if (= (fields [(head field-ids) "name"]) field-name)
        (head field-ids)
        (recur (tail field-ids))))))

;;Function to change fields types
;;It accepts a default type and a list of [field, type] pairs:
;; e.g.: [["field", "categorical"], ["field2", "numeric"]]
(define (change-field-types source-id base-type explicit-types)
  (if (not (list? explicit-types))
    (raise "Explicit types must be specified as a list of pairs")
    (let (source (fetch source-id)
          fields (resource-fields source)
          field-ids (keys fields)
          new-types (iterate (new-types {} field-id field-ids)
                      (assoc new-types field-id {"optype" base-type}))
          new-types (iterate (new-types new-types pair explicit-types)
                      (assoc new-types (get-field-id fields (pair 0)) {"optype" (pair 1)})))
      (update source-id {"fields" new-types}))))
      
(change-field-types source-id base-type explicit-types)