printing levels of a tree on separate lines

DFS.purs

-- Solution 2: using breadth-first search

module Main where

import Prelude

import Data.Array as Array
import Data.Foldable (foldM, traverse_)
import Data.Traversable (traverse)
import Data.Tuple.Nested ((/\))
import Effect (Effect)
import Effect.Class.Console as Console

data Tree a = B a (Array (Tree a))

printLevels :: forall a. Show a => Tree a -> Effect Unit
printLevels t = go [ t ]
  where
  go ts | Array.null ts = pure unit
  go ts = do
    as /\ ts' <- ts
      # foldM
          ( \(as /\ ts') (B a ts'') -> do
              pure $ (as <> [ a ]) /\ (ts' <> ts'')
          )
          ([] /\ [])
    Console.logShow as
    go ts'

MergeLevels.purs

-- Solution 1: using mergeLevels

module MergeLevels where

import Prelude

import Data.Array as Array
import Data.Foldable (traverse_)
import Effect (Effect)
import Effect.Class.Console as Console

data Tree a = B a (Array (Tree a))

printLevels :: forall a. Show a => Tree a -> Effect Unit
printLevels t = printLevels' t # traverse_ Console.logShow

printLevels' :: forall a. Show a => Tree a -> Array (Array String)
printLevels' (B a ts) = [ show a ] Array.: (ts # map printLevels' # mergeLevels)

mergeLevels :: Array (Array (Array String)) -> Array (Array String)
mergeLevels = Array.foldl f []
  where
  f ls1 ls2 = Array.zipWith append ls1 ls2 <>
    ( if Array.length ls1 < Array.length ls2 then
        Array.drop (Array.length ls1) ls2
      else
        Array.drop (Array.length ls2) ls1
    )