# vim first: :s/ //g

:import std/Combinator .
:import std/Char C
:import std/String S
:import std/Pair P
:import std/Number .
:import std/List .

direction! [^0 : (S.string→number ~0)] ⧗ (List Char) → Direction

:test (direction! "R42") ('R' : (+42))

# north=0, east=1, south=2, west=3
# rotation : (x : y)
start ((+0) : ((+0) : (+0))) ⧗ State

move [[go ((C.eq? ^0 'R' ++‣ --‣) ^1)]] ⧗ State → Direction → State
	go [0 : (even? 0 y x)]
		x (^(~2) + (p ~1)) : ~(~2)
			p ((0 % (+4)) =? (+3)) -‣ [0]
		y ^(~2) : (~(~2) + (p ~1))
			p ((0 % (+4)) =? (+2)) -‣ [0]

:test (move start (direction! "R42")) ((+1) : ((+42) : (+0)))

part1 (P.uncurry …+…) ∘ ~‣ ∘ (foldl move start) ⧗ (List Direction) → State

main [parts coords]
	coords direction! <$> (split-list-by [C.eq? 0 ','] (init 0))
	parts [(part1 0)]