Tree and map

functional-tree.ts

import * as O from 'fp-ts/Option'
import { pipe } from 'fp-ts/function'

// interface Tree<A> {
type Tree<A> = {
  readonly left: O.Option<Tree<A>>
  readonly data: A
  readonly right: O.Option<Tree<A>>
}
const subt: Tree<number> = { left: O.none, data: 7, right: O.none }
const t: Tree<number> = {
  left: O.some(subt),
  data: 5,
  right: O.none
}
const treeMap = <A, B>(f: (a: A) => B) => (ts: Tree<A>): Tree<B> => {
  return  { 
    data: f(ts.data),
    left: O.map(treeMap(f))(ts.left),
    right: O.map(treeMap(f))(ts.right),
  }
}
const mapResult = treeMap<number, number>(x => x * 3)(t)
mapResult