feat: allow adding Node as child of Node

src/LeftChildRightSiblingTrees.jl

@@ -13,7 +13,8 @@ export Node,
     isleaf,
     islastsibling,
     lastsibling,
-    prunebranch!
+    prunebranch!,
+    copy_subtree
 
 mutable struct Node{T}
     data::T
@@ -100,6 +101,50 @@ function addchild(parent::Node{T}, data) where T
     newc
 end
 
+"""
+    child = addchild(parent::Node{T}, data::Node{T}) where {T}
+
+Add a node `data` as the last child of `parent`. Requires that `data` is a root node.
+"""
+function addchild(parent::Node{T}, data::Node{T}) where T
+    if !isroot(data)
+        error("Child node must be a root node")
+    end
+    prevc = parent.child
+    if prevc == parent
+        parent.child = data
+    else
+        prevc = lastsibling(prevc)
+        prevc.sibling = data
+    end
+    data.parent = parent
+    data
+end
+
+"""
+    new_root = copy_subtree(root::Node{T}) where {T}
+
+Get a shallow copy of the subtree rooted at `root`. Note that this does not copy the
+data, and only copies the tree structure.
+"""
+function copy_subtree(root::Node{T}) where {T}
+    new_root = Node{T}(root.data)
+    if !isleaf(root)
+        last_child = new_root
+        for child in root
+            new_child = copy_subtree(child)
+            if last_child === new_root
+                new_root.child = new_child
+            else
+                last_child.sibling = new_child
+            end
+            new_child.parent = new_root
+            last_child = new_child
+        end
+    end
+    return new_root
+end
+
 """
     isroot(node)
 
@@ -239,7 +284,7 @@ function Base.:(==)(a::Node, b::Node)
     reta, retb = iterate(a), iterate(b)
     while true
         reta === retb === nothing && return true
-        (reta === nothing) || (retb === nothing) && return false
+        ((reta === nothing) || (retb === nothing)) && return false
         childa, statea = reta
         childb, stateb = retb
         childa == childb || return false

test/runtests.jl

@@ -104,6 +104,38 @@ end
     c = collect(tree1)
     addchild(last(c), "Kid")
     @test tree1 != tree2
+
+    root = Node(1)
+    otherroot = Node(2)
+    addchild(otherroot, 3)
+    addchild(otherroot, 4)
+    newc = addchild(root, otherroot)
+    @test newc === otherroot
+    @test !isleaf(root)
+    @test depth(root) == 3
+    @test map(x -> x.data, collect(PreOrderDFS(root))) == [1, 2, 3, 4]
+    tmp = Node(0)
+    @test_throws ErrorException addchild(tmp, otherroot)
+    thirdroot = Node(5)
+    addchild(thirdroot, 6)
+    addchild(thirdroot, 7)
+    newc = addchild(root, thirdroot)
+    @test newc === thirdroot
+    @test map(x -> x.data, collect(PreOrderDFS(root))) == [1, 2, 3, 4, 5, 6, 7]
+
+    @test !islastsibling(otherroot)
+    copied_root = copy_subtree(otherroot)
+    @test AbstractTrees.isroot(copied_root)
+    @test islastsibling(copied_root)
+    for (oldchild, newchild) in zip(otherroot, copied_root)
+        @test oldchild.parent === otherroot
+        @test newchild.parent === copied_root
+    end
+
+    leaf = Node(2)
+    copied_leaf = copy_subtree(leaf)
+    @test isleaf(leaf)
+    @test isleaf(copied_leaf)
 end
 
 @testset "AbstractTrees" begin