Common Lisp Extensions
11.2 Substitution of Expressions
These functions substitute elements throughout a tree of cons
cells. (See section 10.3 Sequence Functions, for the substitute
function, which works on just the top-level elements of a list.)
- Function: subst new old tree &key :test :test-not :key
- This function substitutes occurrences of old with new
in tree, a tree of cons cells. It returns a substituted
tree, which will be a copy except that it may share storage with
the argument tree in parts where no substitutions occurred.
The original tree is not modified. This function recurses
on, and compares against old, both
cars and cdrs
of the component cons cells. If old is itself a cons cell,
then matching cells in the tree are substituted as usual without
recursively substituting in that cell. Comparisons with old
are done according to the specified test (eql by default).
The :key function is applied to the elements of the tree
but not to old.
- Function: nsubst new old tree &key :test :test-not :key
- This function is like
subst, except that it works by
destructive modification (by setcar or setcdr)
rather than copying.
The subst-if, subst-if-not, nsubst-if, and
nsubst-if-not functions are defined similarly.
- Function: sublis alist tree &key :test :test-not :key
- This function is like
subst, except that it takes an
association list alist of old-new pairs.
Each element of the tree (after applying the :key
function, if any), is compared with the cars of
alist; if it matches, it is replaced by the corresponding
cdr.
- Function: nsublis alist tree &key :test :test-not :key
- This is a destructive version of
sublis.
