presto-main/src/main/java/io/prestosql/sql/planner/plan/Assignments.java/Assignments/rewrite
class Assignments:    public Assignments rewrite(Function<Expression, Expression> rewrite)
    {
        return assignments.entrySet().stream()
                .map(entry -> Maps.immutableEntry(entry.getKey(), rewrite.apply(entry.getValue())))
                .collect(toAssignments());
    }