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(elisp)Modifying Lists

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Modifying Existing List Structure
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   You can modify the CAR and CDR contents of a cons cell with the
primitives `setcar' and `setcdr'.  We call these "destructive"
operations because they change existing list structure.

     Common Lisp note: Common Lisp uses functions `rplaca' and `rplacd'
     to alter list structure; they change structure the same way as
     `setcar' and `setcdr', but the Common Lisp functions return the
     cons cell while `setcar' and `setcdr' return the new CAR or CDR.

Setcar

Replacing an element in a list.

Setcdr

Replacing part of the list backbone.

This can be used to remove or add elements.

Rearrangement

Reordering the elements in a list; combining lists.