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# Let's define a Tree
Tree = Algebrick.type do |tree|
variants Empty = type,
Leaf = type { fields Integer },
Node = type { fields tree, tree }
end # => Tree(Empty | Leaf | Node)
# Values of atomic types are represented by itself,
# they are theirs own value.
Empty.kind_of? Algebrick::Value # => true
Empty.kind_of? Algebrick::Type # => true
Empty.kind_of? Empty # => true
# Values of product types are constructed with #[] and they are immutable.
Leaf[1].kind_of? Algebrick::Value # => true
Leaf[1].kind_of? Leaf # => true
Node[Empty, Empty].kind_of? Node # => true
# Variant does not have its own values, it uses atoms and products.
Leaf[1].kind_of? Tree # => true
Empty.kind_of? Tree # => true
# Product can have its fields named.
BinaryTree = BTree = Algebrick.type do |btree|
fields! value: Integer, left: btree, right: btree
variants Tip = atom, btree
end
# => BTree(Tip | BTree(value: Integer, left: BTree, right: BTree))
# Then values can be created with names
tree1 = BTree[value: 1, left: Tip, right: Tip]
# => BTree[value: 1, left: Tip, right: Tip]
# or without them as before.
BTree[0, Tip, tree1]
# => BTree[value: 0, left: Tip, right: BTree[value: 1, left: Tip, right: Tip]]
# Fields of products can be read as follows:
# 1. When type has only one field method #value is defined
Leaf[1].value # => 1
# 2. By multi-assign
v, left, right = BTree[value: 1, left: Tip, right: Tip]
# => BTree[value: 1, left: Tip, right: Tip]
[v, left, right] # => [1, Tip, Tip]
# 3. With #[] method when fields are named
BTree[value: 1, left: Tip, right: Tip][:value] # => 1
BTree[value: 1, left: Tip, right: Tip][:left] # => Tip
# 4. With methods named by fields when fields are named
# (it can be disabled if fields are defined with #fields instead of #fields!)
BTree[1, Tip, Tip].value # => 1
BTree[1, Tip, Tip].left # => Tip
# Product instantiation raises TypeError when being constructed with wrong type.
Leaf['a'] rescue $!
# => #<TypeError: Value (String) 'a' is not any of: Integer.>
Node[nil, Empty] rescue $!
# => #<TypeError: Value (NilClass) '' is not any of: Tree(Empty | Leaf | Node).>
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