My first initial encoding of the Id monad with a stack safe interpreter

id_encoding.js

const FlatMap = (ma, famb) => ({
  ma,
  famb,
  tag: 'FlatMap'
})

const Pure = (a) => ({ a, tag: 'Pure' })

const expression = FlatMap(
  FlatMap(
    Pure(6),
    n => Pure(n)
  ),
  n => FlatMap(
    Pure(24),
    m => Pure(n + m)
  )
)

function interpreter(m) {
  
  const stack = []
  let curr = m
  
  while(true) {
     switch(curr.tag) {
      case 'FlatMap': {
        stack.push(curr.famb)
        curr = curr.ma
        break;
      }
      case 'Pure': {
        if(stack.length == 0) return curr.a
        else {
          const cont = stack.pop()
          curr = cont(curr.a)
        }
        break;
      }
    } 
  }
}

interpreter(expression)