Combine child and internal child

Binds two parse tables together and arranges them so that the tokens are in the correct order.

combine_children(child, internal_child)

Arguments

child	A parse table or NULL.
internal_child	A parse table or NULL.

Details

Essentially, this is a wrapper around dplyr::bind_rows(), but returns NULL if the result of dplyr::bind_rows() is a data frame with zero rows.