Replace a subtree with a leaf:

Replace a subtree at any position:

Replace subtrees at several positions:

Replace each position with a different subtree:

Replace subtrees whose positions match a pattern:

Use the operator form of TreeReplacePart:

Patterns can represent part lists of variable length:

Replacing a subtree with an expression other than a Tree object is equivalent to inserting a leaf:

The expression x is inserted as the leaf

:

Replace a subtree with several subtrees using Splice:

Subtrees can be replaced, as well as inserted or deleted:

Construct a tree from the heads in an expression:

TreeReplacePart replaces a subtree of a tree:

This corresponds to replacing a subexpression of an expression:

ReplacePart can replace subexpressions directly:

If pos is not a list, pos and {pos} are equivalent specifications:

A pattern p that is not explicitly a list matches against the immediate children:

In that case, p is equivalent to {p}:

Replacing position {} replaces the whole tree:

TreeReplacePart uses rules in the order given:

TreeReplacePart can use the lists of positions returned by TreePosition:

These are the subtrees returned by TreeExtract:

TreeReplacePart[tree,{p₁,p₂,…}new] treats {p₁,p₂,…} as a list of individual position specifications if all the p_i are lists:

For {{1,2},{3,4}}, the subtrees at positions {1,2} and {3,4} are replaced:

If any p_i is not a list, {p₁,p₂,…} is treated as a list of part specifications:

For {{{1,2},{3,4}}}, parts 3 and 4 of parts 1 and 2 are replaced:

TreeReplacePart only affects positions that are already present:

TreeReplacePart[tree,{}new] does not replace any subtrees because the list of positions is empty:

TreeReplacePart[tree,{{}}new] replaces position {}, which corresponds to the whole tree: