tree.ts

tree.ts

interface Tree<A> {
  readonly value: A
  readonly forest: Forest<A>
}
​
type Forest<A> = Array<Tree<A>>
​
const draw = (indentation: string, forest: Forest<string>): string => {
  let r: string = ''
  const len = forest.length
  let tree: Tree<string>
  for (let i = 0; i < len; i++) {
    tree = forest[i]
    const isLast = i === len - 1
    r += indentation + (isLast ? '└' : '├') + '─ ' + tree.value
    r += draw(indentation + (len > 1 && !isLast ? '│  ' : '   '), tree.forest)
  }
  return r
}
​
const drawForest = (forest: Forest<string>): string => draw('\n', forest)
​
const drawTree = (tree: Tree<string>): string => tree.value + drawForest(tree.forest)
​
const make = <A>(value: A, forest: Forest<A> = []): Tree<A> => ({
  value,
  forest,
})
​
interface Predicate<A> {
  (a: A): boolean
}
​
const splitAt =
  <A>(n: number) =>
  (xs: Array<A>): [A[], A[]] =>
    [xs.slice(0, n), xs.slice(n)]
​
const until =
  <A>(p: Predicate<A>) =>
  (f: (a: A) => A) =>
  (x: A): A => {
    let v = x
    while (!p(v)) {
      v = f(v)
    }
​
    return v
  }
​
const succ = (x: number) => 1 + x
​
const span =
  <A>(p: Predicate<A>) =>
  (xs: Array<A>): [A[], A[]] => {
    const iLast = xs.length - 1
​
    return splitAt<A>(until<number>(i => iLast < i || !p(xs[i]))(succ)(0))(xs)
  }
​
const forestFromLineIndents = (tuples: Array<[number, string]>) => {
  const go = (xs: Array<[number, string]>): Forest<string> =>
    0 < xs.length
      ? (() => {
          const [n, s] = Array.from(xs[0]) as [number, string]
          const [firstTreeLines, rest] = Array.from(span<[number, string]>(x => n < x[0])(xs.slice(1)))
​
          return [make(s, go(firstTreeLines))].concat(go(rest))
        })()
      : []
​
  return go(tuples)
}
​
const treeFromText = (text: string): Tree<string> =>
  make('.', forestFromLineIndents(text.split('\n').map(x => [Math.ceil(x.search(/\S/) / 2), x.trimStart()])))
​
const text = `Edit me to generate
  a
    nice
      tree
        diagram!
        :)
  Use indentation
    to indicate
      file
      and
      folder
      nesting.
    - You can even
      - use
        - markdown
        - bullets!`
​
console.log(drawTree(treeFromText(text)))
​
// outputs:
//
// .
// └─ Edit me to generate
//    ├─ a
//    │  └─ nice
//    │     └─ tree
//    │        ├─ diagram!
//    │        └─ :)
//    └─ Use indentation
//       ├─ to indicate
//       │  ├─ file
//       │  ├─ and
//       │  ├─ folder
//       │  └─ nesting.
//       └─ - You can even
//          └─ - use
//             ├─ - markdown
//             └─ - bullets!