Tree/Rose.bruijn

# MIT License, Copyright (c) 2023 Marvin Borner
# Rose trees based on std/List

:import std/Combinator .
:import std/List L
:import std/Logic .
:import std/Math .
:import std/Pair .

# a tree node has a label as its head and subtrees as its tail

# constructs a tree with a label and no branches
leaf [0 : L.empty] ⧗ a → (RoseTree a)

{:}‣ leaf

# constructs a node with subnodes
node [[1 : 0]] ⧗ a → (List (RoseTree a)) → (RoseTree a)

{…:…} node

# returns the root label of a tree
label ^‣ ⧗ (RoseTree a) → a

^‣ label

# returns the branches of a tree
branches ~‣ ⧗ (RoseTree a) → (List (RoseTree a))

~‣ branches

# returns true if a tree is empty
empty? [L.empty? ~0] ⧗ (RoseTree a) → Boolean

∅?‣ empty?

:test (∅?({ 'a' : ({:}'b' : L.empty) })) (false)
:test (∅?({:}'a')) (true)

# applies a function to leaf and the leafs of all branches
map z [[[rec]]] ⧗ (a → b) → (RoseTree a) → (RoseTree b)
	rec { (1 ^0) : (L.map (2 1) ~0) }

…<$>… map

:test (map ^‣ ({ "woo" : ({:}"oof" : (({ "aah" : ({:}"huh" : L.empty) }) : L.empty)) })) ({ 'w' : ({:}'o' : (({ 'a' : ({:}'h' : L.empty) }) : L.empty)) })

# maps a function returning list of trees and concatenates
concat-map L.concat ∘∘ map ⧗ ((RoseTree a) → (List (RoseTree b))) → (List (RoseTree a)) → (List (RoseTree b))

# folds a tree
# TODO: fix
fold [[[z [[rec]] 0]]] ⧗ (a → (List b) → b) → (RoseTree a) → b
	rec ∅?0 case-end case-fold
		case-fold 4 ^0 (1 ~0)
		case-end 3

# :test (fold [[∅?0 (+1) (sum 0)]] ({ 'w' : ({:}'o' : (({ 'a' : ({:}'h' : L.empty) }) : L.empty)) })) ((+4))