I’m new to this discourse and really Purescript. I took a few tries at learning FP, first with Haskell, then with Purescript and I think I’m finally making headway in a substantial way.
To put the skills into practice I took adventofcode as a playground. Not long into the puzzles and I can’t seem to solve a problem due to recursion and I’m not there yet with different monads to be able to solve it with State/ST/Ref yet so I’d really appreciate some pointers.
The problem is:
— Day 7: Some Assembly Required —
This year, Santa brought little Bobby Tables a set of wires and bitwise logic gates! Unfortunately, little Bobby is a little under the recommended age range, and he needs help assembling the circuit.
Each wire has an identifier (some lowercase letters) and can carry a 16-bit signal (a number from
65535 ). A signal is provided to each wire by a gate, another wire, or some specific value. Each wire can only get a signal from one source, but can provide its signal to multiple destinations. A gate provides no signal until all of its inputs have a signal.
The included instructions booklet describes how to connect the parts together:
x AND y -> z means to connect wires
y to an AND gate, and then connect its output to wire
123 -> xmeans that the signal
123is provided to wire
x AND y -> zmeans that the bitwise AND of wire
yis provided to wire
p LSHIFT 2 -> qmeans that the value from wire
pis left-shifted by
2and then provided to wire
NOT e -> fmeans that the bitwise complement of the value from wire
eis provided to wire
Other possible gates include
OR (bitwise OR) and
For example, here is a simple circuit:
123 -> x 456 -> y x AND y -> d x OR y -> e x LSHIFT 2 -> f y RSHIFT 2 -> g NOT x -> h NOT y -> i
After it is run, these are the signals on the wires:
d: 72 e: 507 f: 492 g: 114 h: 65412 i: 65079 x: 123 y: 456
In little Bobby’s kit’s instructions booklet (provided as your puzzle input), what signal is ultimately provided to wire
And my solution is https://github.com/razcore-art/adventofcode/blob/master/src/AOC2015/D07.purs. Which I’m also pasting here for easier access:
module AOC2015.D07 where import Prelude import Data.Array (catMaybes) import Data.Function.Memoize (memoize) import Data.Generic.Rep (class Generic) import Data.Generic.Rep.Show (genericShow) import Data.Int (fromString) import Data.Int.Bits (complement, shl, shr, (.&.), (.|.)) import Data.Map (Map) import Data.Map as M import Data.Maybe (Maybe(..)) import Data.String (Pattern(..), split, trim) import Data.Traversable (sequence) import Data.Tuple (Tuple(..)) data Wire = Constant Int | Link String | And String String | Or String String | Not String | LShift String Int | RShift String Int derive instance genericWire :: Generic Wire _ instance showWire :: Show Wire where show = genericShow input :: String input = """ ... """ input' :: Map String Wire input' = M.fromFoldable <<< catMaybes $ sequence <$> catMaybes do arr <- map trim <<< split (Pattern "->") <$> (split (Pattern "\n") $ trim input) pure case arr of [expr, key] -> Just (Tuple key $ wireExpr expr) _ -> Nothing where wireExpr :: String -> Maybe Wire wireExpr s = case split (Pattern " ") s of [a, "AND", b] -> Just $ And (trim a) (trim b) [a, "OR", b] -> Just $ Or (trim a) (trim b) [a, "LSHIFT", b] -> LShift (trim a) <$> fromString b [a, "RSHIFT", b] -> RShift (trim a) <$> fromString b ["NOT", a ] -> Just $ Not (trim a) [a ] -> case fromString a of Just i -> Just $ Constant i Nothing -> Just $ Link a _ -> Nothing eval :: Map String Wire -> String -> Int eval m k = case memoize (flip M.lookup m) k of Just (Constant i ) -> i Just (Link a ) -> eval m a Just (And a b) -> eval m a .&. eval m b Just (Or a b) -> eval m a .|. eval m b Just (Not a ) -> complement $ eval m a Just (LShift a i) -> shl (eval m a) i Just (RShift a i) -> shr (eval m a) i Nothing -> 0 part1 :: Int part1 = memoize (eval input') "a" part2 :: String part2 = "TODO"
Which works fine on made-up “instruction” input and the example. But on the long puzzle input, it takes forever. As you can see I tried using
memoize, but it doesn’t seem to improve anything. I also tried using
trace from the
debug module, but it didn’t print out anything in the
eval recursive function, instead it pushes Purescript to error out, I didn’t save the error.
So, I’m pretty sure this is because Purescript is not a lazy language, I just don’t know how to make it work so any help is appreciated.