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fold()

fold<T, R>(node, handlers): R

Folds over a composite tree, reducing it to a single value. This replaces the recursive operation() method from OOP Composite.

Type Parameters​

T: T​

The data type in nodes

R: R​

The result type

Parameters​

node: Composite<T>​

The root node to fold

handlers: FoldHandlers<T, R>​

Functions to handle leaf and branch nodes

Returns: R​

The folded result

Since​

2.4.0

Example​

// Count all nodes
const count = fold(tree, {
  leaf: () => 1,
  branch: (_, children) => 1 + children.reduce((a, b) => a + b, 0),
});

// Render to string
const render = fold(tree, {
  leaf: (data) => data.name,
  branch: (data, children) => `${data.name}(${children.join(", ")})`,
});

FoldHandlers<T, R>​

Type

FoldHandlers<T, R> = object

Handlers for folding over a composite tree.

Since​

2.4.0

Type Parameters​

T: T​

The data type in nodes

R: R​

The result type

Properties​

leaf(): (data) => R​

Handle a leaf node. Receives the leaf's data.

data: T
Returns: R

branch(): (data, childResults) => R​

Handle a branch node. Receives the branch's data and results from children.

data: T
childResults: R[]
Returns: R

Composite<T>​

Type

Composite<T> = Leaf<T> | Branch<T>

A Composite is either a Leaf or a Branch. This discriminated union replaces the OOP Component/Leaf/Composite hierarchy.

Type Parameters​

T: T​

The data type stored in nodes

Since​

2.4.0