gmapQ

A generic query that processes the immediate subterms and returns a list of results. The list is given in the same order as originally specified in the declaration of the data constructors.
A generic query that processes one child by index (zero-based)
A generic query with a left-associative binary operator
A generic query with a right-associative binary operator
Use children and !!
Use children and foldl
Use children and foldr