/usr/local/lib/swipl/library/terms.pl
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 mapsubterms(:Goal, +Term1, -Term2) is det
 mapsubterms_var(:Goal, +Term1, -Term2) is det
Recursively map sub terms of Term1 into subterms of Term2 for every pair for which call(Goal, ST1, ST2) succeeds. Procedurably, the mapping for each (sub) term pair T1/T2 is defined as:
  • If T1 is a variable
  • If call(Goal, T1, T2) succeeds we are done. Note that the mapping does not continue in T2. If this is desired, Goal must call mapsubterms/3 explicitly as part of its conversion.
  • If T1 is a dict, map all values, i.e., the tag and keys are left untouched.
  • If T1 is a list, map all elements, i.e., the list structure is left untouched.
  • If T1 is a compound, use same_functor/3 to instantiate T2 and recurse over the term arguments left to right.
  • Otherwise T2 is unified with T1.

Both predicates are implemented using foldsubterms/5.