Provenance functions

Freezes the tracker so that no tracker operations can affect this
particular tracker.

Args:
    val (any): any provenance-tracked (i.e. value-wrapped) Value

Returns:
    the same value with the provenance frozen

Examples:
    my_udf(freeze(field_1)) -> the output of your udf with the same provenance as field_1

Get provenance information for a provenance-tracked value.
Returns a dictionary of provenance information for the given
Value.

Args:
    val (any): any provenance-tracked (i.e. value-wrapped) Value

Returns:
    a dictionary of provenance information for the given value

Examples:
    provenance_get(field_1)