new—an object.
old—an object.
predicate—a symbol that names a function, or a function of one argument that returns a generalized boolean value.
tree—a tree.
test—a designator for a function of two arguments that returns a generalized boolean.
test-not—a designator for a function of two arguments that returns a generalized boolean.
key—a designator for a function of one argument,
or nil
.
new-tree—a tree.
subst
, subst-if
, and subst-if-not
perform
substitution operations on tree.
Each function searches tree for occurrences of a
particular old item of an element or subexpression that
satisfies the test.
nsubst
, nsubst-if
, and nsubst-if-not
are
like subst
,
subst-if
, and subst-if-not
respectively, except that the
original tree is modified.
subst
makes a copy of tree,
substituting new for every subtree or leaf of tree
(whether the subtree or leaf is a car or a cdr of its parent)
such that old and the subtree or leaf satisfy the test.
nsubst
is a destructive version of subst
.
The list structure of
tree is altered by destructively replacing with new
each leaf of the tree such that old and the leaf
satisfy the test.
For subst
, subst-if
,
and subst-if-not
,
if the functions succeed, a new
copy of the tree is returned in which each occurrence of such an
element is replaced by the
new element or subexpression. If no changes are made, the original
tree may be returned.
The original tree is left unchanged, but the result tree
may share storage with it.
For nsubst
, nsubst-if
,
and nsubst-if-not
the original tree is modified and returned as the function result,
but the result may not be eq
to tree.
(setq tree1 '(1 (1 2) (1 2 3) (1 2 3 4))) → (1 (1 2) (1 2 3) (1 2 3 4)) (subst "two" 2 tree1) → (1 (1 "two") (1 "two" 3) (1 "two" 3 4)) (subst "five" 5 tree1) → (1 (1 2) (1 2 3) (1 2 3 4)) (eq tree1 (subst "five" 5 tree1)) → implementation-dependent (subst 'tempest 'hurricane '(shakespeare wrote (the hurricane))) → (SHAKESPEARE WROTE (THE TEMPEST)) (subst 'foo 'nil '(shakespeare wrote (twelfth night))) → (SHAKESPEARE WROTE (TWELFTH NIGHT . FOO) . FOO) (subst '(a . cons) '(old . pair) '((old . spice) ((old . shoes) old . pair) (old . pair)) :test #'equal) → ((OLD . SPICE) ((OLD . SHOES) A . CONS) (A . CONS)) (subst-if 5 #'listp tree1) → 5 (subst-if-not '(x) #'consp tree1) → (1 X) tree1 → (1 (1 2) (1 2 3) (1 2 3 4)) (nsubst 'x 3 tree1 :key #'(lambda (y) (and (listp y) (third y)))) → (1 (1 2) X X) tree1 → (1 (1 2) X X)
nsubst
, nsubst-if
, and nsubst-if-not
might alter the tree structure of tree.
substitute, nsubstitute, Section 3.2.1 (Compiler Terminology), Section 3.6 (Traversal Rules and Side Effects)
The :test-not parameter is deprecated.
The functions subst-if-not
and nsubst-if-not
are deprecated.
One possible definition of subst
:
(defun subst (old new tree &rest x &key test test-not key) (cond ((satisfies-the-test old tree :test test :test-not test-not :key key) new) ((atom tree) tree) (t (let ((a (apply #'subst old new (car tree) x)) (d (apply #'subst old new (cdr tree) x))) (if (and (eql a (car tree)) (eql d (cdr tree))) tree (cons a d))))))