expand_goal(+Goal1, ?Layout1, -Goal2, -Layout2)

goal_expansion(+Goal1, ?Layout1, -Goal2, -Layout2)

expand_term(+Term1, ?Layout1, -Term2, -Layout2)

term_expansion(+Term1, ?Layout1, -Term2, -Layout2)

dcg_translate_rule(+In, ?LayoutIn, -Out, -LayoutOut)

These versions are called before their 2-argument counterparts. The input layout term is either a variable (if no layout information is available) or a term carrying detailed layout information as returned by the subterm_positions of read_term/2. The output layout should be a variable if no layout information can be computed for the expansion; a sub-term can also be a variable to indicate “don't know” .