diff --git a/README.md b/README.md index 95cd2ee..6dfd540 100644 --- a/README.md +++ b/README.md @@ -1,10 +1,25 @@ # Advent The goal of this project is to get all 500 currently available stars in the form -of one single idris application, and thoroughly document the results as literate -idris files. +of one single Idris application, and thoroughly document the results as literate +Idris files. -# Index of non-day modules +## Authors Note + +The solutions contained in this project are intended to be read in sequential +order, though can reasonably be read in any order if you have a good level of +familiarity with more advanced functional programming topics. + +The solutions will involve progressively more advanced topics as day and year +number increase, though I try not to introduce too much within the scope of any +one day. + +Suggestions and other feedback are highly welcome, please reach out to me via +any platform you know me on, or send an email to the +[~thatonelutenist/public-inbox](https://lists.sr.ht/~thatonelutenist/public-inbox) +mailing list on source hut. + +## Index of non-day modules - [Runner](src/Runner.md) @@ -26,16 +41,61 @@ solution. Extend the functionality of the effects included in the [eff](https://github.com/stefan-hoeck/idris2-eff/) library -# Index of years and days + - [Util.Digits](src/Util/Digits.md) + + Provide views that enable recursively pattern matching numbers as lists of + digits, in both ascending and descending order of significance. + +## Index of years and days - 2015 - [Day 1](src/Years/Y2015/Day1.md) + + Warm up problem, breaks in our new runner and not much else interesting. + - [Day 2](src/Years/Y2015/Day2.md) + + An early hint of effectful parsing. + - [Day 3](src/Years/Y2015/Day3.md) + + Peculiarities of writing mutually recursive functions in dependently typed + languages. + - [Day 4](src/Years/Y2015/Day4.md) + + Basic FFI to openssl to steal its MD5 function for Idris's use. + - [Day 5](src/Years/Y2015/Day5.md) + + First introduction to views and dependent pattern matching[^1]. + - [Day 6](src/Years/Y2015/Day6.md) + + Naive approach to handling the first 2d grid problem. + - [Day 7](src/Years/Y2015/Day7.md) + + Introduces dependent maps and indexed type families. + - [Day 8](src/Years/Y2015/Day8.md) + + Proper effectful parsers and non-determinism in effect stacks. + - [Day 9](src/Years/Y2015/Day9.md) + + Naive approach to handling the first graph traversal problem. + - [Day 10](src/Years/Y2015/Day10.md) + + Introduce our `Digits`, dependent pattern matching on integers as lists of + digits. + + - [Day 11](src/Years/Y2015/Day11.md) + + Introduces refinement types + +## References + +[^1]: Idris 2 Manual: + [Views and the "with" rule](https://idris2.readthedocs.io/en/latest/tutorial/views.html#views-and-the-with-rule) diff --git a/advent.ipkg b/advent.ipkg index e915d93..c9776ba 100644 --- a/advent.ipkg +++ b/advent.ipkg @@ -21,6 +21,7 @@ depends = base , ansi , if-unsolved-implicit , c-ffi + , refined -- modules to install modules = Runner diff --git a/src/Grid.md b/src/Grid.md deleted file mode 100644 index ceb6a22..0000000 --- a/src/Grid.md +++ /dev/null @@ -1,371 +0,0 @@ -# 2D Grid utilities - -Types and utilities for dealing with a 2D grid of things - -We base our `Grid` type on `Data.Seq.Sized` from `contrib`, a finger tree based -collection that tracks its size in its type, since it provides somewhat -efficient random access and updates. - -```idris -module Grid - -import Data.Seq.Sized -import Data.Fin -import Data.Fin.Extra -import Data.List.Lazy -import Data.Zippable -import Data.Vect -import Data.String -import Decidable.Equality - -%default total -``` - -## Coordinates - -A coordinate is a pair of numbers both less than their respective bounds. - -Since `Grid`s will always be non-empty in the contexts we will be using them in, -this type alias adds one to each of the bounds to ensure non-emptyness - -```idris -public export -Coord : (rows, cols : Nat) -> Type -Coord rows cols = (Fin (S rows), Fin (S cols)) -``` - -### Coordinate utility functions - -Lazily generate all the coordinates for a given pair of bounds - -Uses an internal helper function to generate a lazy list of all the fins of a -given bound in ascending order (`all`), and another to convert a lazy list of -`Fin` into a lazy list of pairs of `Fin`s. - -The totality checker likes to go in the descending direction, since then it can -reason about values getting structurally "smaller", so it has issues with `all'` -moving in the ascending direction. We know this function is total because the -`acc < last` check will always eventually be triggered, since `Fin`s only have a -finite number of values. - -We pull out an `assert_smaller` to tell Idris that the argument to the recursive -call is getting structurally smaller, which while not strictly correct, does -convey to the compiler that we are getting closer to our recursive base case and -that the function is thus total. - -```idris -export -allCords : {rows, cols : Nat} -> LazyList (Coord rows cols) -allCords = concat . map row $ all - where - all : {n : Nat} -> LazyList (Fin (S n)) - all = FZ :: all' FZ - where - all' : {n : Nat} -> (acc : Fin (S n)) -> LazyList (Fin (S n)) - all' acc = - if acc < last - then finS acc :: all' (assert_smaller acc (finS acc)) - else [] - row : Fin (S rows) -> LazyList (Coord rows cols) - row r = map (\c => (r, c)) all -``` - -Add a given vector to a coordinate, returning `Nothing` if we go off the ends of -the bounds in the process. - -To keep this function simple and reasonably efficient, we perform the arithmetic -in integer space, using `integerToFin` to fallably convert back to `Fin` space, -making use of the `Maybe` monad to keep the code clean. - -```idris -export -step : {rows, cols : Nat} -> (input : Coord rows cols) -> (direction : (Integer, Integer)) - -> Maybe (Coord rows cols) -step (row, col) (d_row, d_col) = do - let (row, col) = (finToInteger row, finToInteger col) - row <- integerToFin (row + d_row) (S rows) - col <- integerToFin (col + d_col) (S cols) - pure (row, col) -``` - -## Grid - -A grid is a `Seq` of `Seq`s with the given size bounds. - -The inner `Seq`s are kept opaque to maintain flexability in the implementation - -```idris -export -record Grid (rows, cols : Nat) (e : Type) where - constructor MkGrid - grid : Seq (S rows) (Seq (S cols) e) -%name Grid grid, grid2, grid3 -``` - -### Constructors - -Construct a `Grid` by filling every slot with identical copies of the provided -element - -```idris -export -replicate : {rows, cols : Nat} -> (seed : e) -> Grid rows cols e -replicate seed = - let row = replicate (S cols) seed - grid = replicate (S rows) row - in MkGrid grid -``` - -Attempt to construct a `Grid` from a Foldable of Foldables. Will return -`Nothing` if either the rows are of heterogeneous size, or if either the rows or -columns are empty. Requires that the outer Foldable also be Traversable. - -We make heavy use of the `Maybe` monad to keep the code clean here. - -```idris -export -fromFoldable : Traversable a => Foldable a => Foldable b => a (b e) -> - Maybe (rows : Nat ** cols : Nat ** Grid rows cols e) -fromFoldable xs = do - -- First collect the number of rows from the outer foldable - let (S rows) = foldl (\acc, e => acc + 1) 0 xs - | _ => Nothing -- Return Nothing if there are no rows - -- Get the number of columns in the largest row in the inner foldable - let (S cols) = foldl (\acco, eo => max acco (foldl (\acci, ei => acci +1) 0 eo)) 0 xs - | _ => Nothing -- Return Nothing if all the rows are empty - -- Convert the rows by traversing our foldToSeq function over the outer foldable - xs <- traverse (foldToSeq (S cols)) xs - -- Reuse our foldToSeq helper function to convert the outer foldable - xs <- foldToSeq (S rows) xs - -- wrap it up and return - pure (rows ** cols ** MkGrid xs) - where - -- Convert each row to a seq using an intermediate list - foldToSeq : Foldable c => (n : Nat) -> c f -> Maybe (Seq n f) - foldToSeq n x = - let list = toList x - -- Check to see if the list is of the correct length, then rewrite the - -- output type to match if that's the case, otherwise return Nothing - in case decEq (length list) n of - Yes Refl => Just $ fromList list - No _ => Nothing -``` - -Construct a `Grid` from a non-empty `Vect` of non-empty `Vect`s. To keep the -function simple, we require that both the row and column dimension are known to -be non-zero before calling this constructor. - -```idris -export -fromVect : Vect (S rows) (Vect (S cols) e) -> Grid rows cols e -fromVect xs = MkGrid . fromVect . map fromVect $ xs -``` - -Construct `Grid` containing the coordinate of the location in each location - -```idris -export -coordinateGrid : {rows, cols : Nat} -> Grid rows cols (Coord rows cols) -coordinateGrid = - let row = fromVect $ allFins (S cols) - grid = zip (fromVect $ allFins (S rows)) (replicate _ row) - grid = map (\(x, xs) => map (x,) xs) grid - in MkGrid grid -``` - -### Accessors and Mutators - -Get the value at a specific index in the grid - -```idris -export -index : Coord rows cols -> Grid rows cols e -> e -index (row, col) grid = - index' (index' grid.grid row) col -``` - -Replace the value at a specific index in the grid - -```idris -export -replaceAt : Coord rows cols -> e -> Grid rows cols e -> Grid rows cols e -replaceAt (row, col) x (MkGrid grid) = - let r = index' grid row - r = update (finToNat col) x r @{elemSmallerThanBound col} - grid = update (finToNat row) r grid @{elemSmallerThanBound row} - in MkGrid grid -``` - -Update the value at a specific index in the grid - -```idris -export -updateAt : Coord rows cols -> (e -> e) -> Grid rows cols e -> Grid rows cols e -updateAt (row, col) f (MkGrid grid) = - let r = index' grid row - r = adjust f (finToNat col) r @{elemSmallerThanBound col} - grid = update (finToNat row) r grid @{elemSmallerThanBound row} - in MkGrid grid -``` - -Lazily provide all the values in the grid as a flat collection - -```idris -export -flat : {rows, cols : Nat} -> Grid rows cols e -> LazyList e -flat (MkGrid grid) = - let grid = seqToLazy . map (seqToLazy {n = S cols}) $ grid - grid = grid [] - in foldrLazy (\a, acc => a acc) [] grid - where - seqToLazy : {n : Nat} -> (seq : Seq n a) -> (rest : LazyList a) -> LazyList a - seqToLazy {n = 0} seq rest = rest - seqToLazy {n = (S k)} seq rest = - let (head, tail) = viewl seq - in head :: seqToLazy tail rest -``` - -### Interface Implementations - -#### Show - -```idris -export -{rows, cols : Nat} -> Show e => Show (Grid rows cols e) where - show (MkGrid grid) = - show . toVect . map toVect $ grid -``` - -#### Eq/Ord - -```idris -export -Eq e => Eq (Grid rows cols e) where - (MkGrid grid_x) == (MkGrid grid_y) = grid_x == grid_y - -export -Ord e => Ord (Grid rows cols e) where - compare (MkGrid grid_x) (MkGrid grid_y) = compare grid_x grid_y -``` - -#### Functor - -```idris -export -Functor (Grid rows cols) where - map f (MkGrid grid) = - MkGrid . map (map f) $ grid -``` - -#### Foldable - -Cheeze it a little and use our `flat` function internally here. - -Also, `null` can statically return false, as `Grid` is structurally non-empty - -```idris -export -{rows, cols : Nat} -> Foldable (Grid rows cols) where - foldr f acc grid = foldr f acc (flat grid) - foldl f acc grid = foldl f acc (flat grid) - null _ = False - toList grid = toList (flat grid) -``` - -#### Applicative - -```idris -export -{rows, cols : Nat} -> Applicative (Grid rows cols) where - pure a = replicate a - (MkGrid f) <*> (MkGrid grid) = - MkGrid . map (\(a,b) => a <*> b) . zip f $ grid -``` - -#### Traversable - -```idris -export -{rows, cols : Nat} -> Traversable (Grid rows cols) where - traverse f (MkGrid grid) = - map MkGrid . traverse (traverse f) $ grid -``` - -#### Zippable - -```idris -export -Zippable (Grid rows cols) where - zipWith f (MkGrid grid_x) (MkGrid grid_y) = - let xs = zip grid_x grid_y - in MkGrid . map (\(a,b) => zipWith f a b) $ xs - unzipWith f (MkGrid grid) = - let (xs, ys) = unzip . map (unzipWith f) $ grid - in (MkGrid xs, MkGrid ys) - zipWith3 f (MkGrid as) (MkGrid bs) (MkGrid cs) = - let xs = zip3 as bs cs - in MkGrid . map (\(a, b, c) => zipWith3 f a b c) $ xs - unzipWith3 f (MkGrid grid) = - let (a, b, c) = unzip3 . map (unzipWith3 f) $ grid - in (MkGrid a, MkGrid b, MkGrid c) -``` - -### Extra - -Extensions of the above functionality - -#### Indexing - -Convert this grid to one with both the index of the location and the element in -each location - -```idris -export -indexed : {rows, cols : Nat} -> Grid rows cols e -> Grid rows cols (Coord rows cols, e) -indexed grid = zip coordinateGrid grid -``` - -Same as `flat` above, but indexed - -```idris -export -flatIndexed : {rows, cols : Nat} -> Grid rows cols e -> LazyList (Coord rows cols, e) -flatIndexed = flat . indexed -``` - -#### String functionality - -Attempts to convert a string, with newline delimited rows, to a grid of -characters - -```idris -export -stringToGrid : String -> Maybe (rows : Nat ** cols : Nat ** Grid rows cols Char) -stringToGrid = fromFoldable . map (unpack . trim) . lines . trim -``` - -Converts a grid of chars to a string, delimiting the rows with newlines - -```idris -export -gridToString : Grid rows cols Char -> String -gridToString (MkGrid grid) = unlines . toList . map (pack . toList) $ grid -``` - -#### Conversion - -Convert a grid to a vect of vects - -```idris -export -toVects : {rows, cols : Nat} -> Grid rows cols e -> Vect (S rows) (Vect (S cols) e) -toVects (MkGrid grid) = toVect . map toVect $ grid -``` - -Convert a grid to a list of lists - -```idris -export -toLists : Grid rows cols e -> List (List e) -toLists (MkGrid grid) = toList . map toList $ grid -``` diff --git a/src/Main.md b/src/Main.md index a913135..f602362 100644 --- a/src/Main.md +++ b/src/Main.md @@ -181,8 +181,8 @@ failures doing so. ## Handling the arguments and finding the input Handle the verbosity flag, if it is set, hook our logger up to stderr, otherwise -blackhole the logs. Afterwards, use `logHandler` to introduce the logging -`Writer` into the effects list. +blackhole the logs. Afterwards, use `logHandler` to introduce the `Logger` into +the effects list. ```idris -- If the verbose flag is set, hook up the logging writer to stderr @@ -259,8 +259,8 @@ a `SolveError`, then print out the result, then return, closing out the program. ### Lower logging into the IO component of the effect -This function uses the provided `String -> IO ()` to remove the `Writer` from -the effects list by translating `tell` calls to IO actions within the effect. +Makes use of `Logger`'s `handleLoggerIO` function to "lower" logging actions +into `IO` within the effect. ```idris -- Lowers logging into IO within the effect using the given IO function diff --git a/src/Runner.md b/src/Runner.md index 500821b..31b036e 100644 --- a/src/Runner.md +++ b/src/Runner.md @@ -22,16 +22,15 @@ import public Util.Eff # Effectful Parts The solution to each part of a day is run as an effectful computation, and as -the available effects are meant to be the same across both parts, only varying -in the type of the error value in the `Except` effect, I construct a type level -function to have a single source of truth for this. The `err` type can be any -type with a `Show` implementation, but that constraint will be tacked on in the -next step. +the effect stack is meant to be the same across both parts, only varying in the +type of the error value for the `Except` effect, we construct a type level +function to have a single source of truth. The `err` type can be any type with a +`Show` implementation, but that constraint will be tacked on in the next step. -A `Writer` effect is provided for logging, and a `Reader` effect is provided to -pass in the input, just to make the top level API a little bit cleaner. `IO` is +The `Logger` effect is provided for logging, and a `Reader` effect is provided +to pass in the input, to make the top level API a little bit cleaner. `IO` is also provided, even though the part solutions themselves shouldn't really be -doing any IO, this may come in handy if a part needs `IO` for performance +doing any IO, this will come in handy if a part needs `IO` for performance reasons. ```idris @@ -46,19 +45,19 @@ PartEff err = # The `Day` Record The `Day` type groups together an effectful `part1` computation, an optional -effectful `part2` computation, the day number, and does some type wrangling to -get the type system out of our way on this one. +effectful `part2` computation, and the day number, with some type wrangling to +get the type system out of our way. `part1` and `part2` are allowed independent output and error types, and this record captures `Show` implementations for those output and error types so that -we can display them in `Main` where the `Day` is consumed without having to +we can display them in `Main`, where the `Day` is consumed, without having to actually know what the types are. It is often useful to pass a bit of context, such as the data structures -resulting from parsing, between `part1` and `part2`, and this is achieved by the -erased `ctx` type, which is totally opaque here. The runner code in `Main` will -provide the value of the `ctx` type produced as part of the output of `part1` as -the input of `part2`. +resulting from parsing, between `part1` and `part2`. This is achieved through +the erased `ctx` type, which is totally opaque to the runner. The code in `Main` +will provide the value of the `ctx` type produced as part of the output of +`part1` and as the input of `part2`. ```idris ||| Model solving a single day @@ -80,9 +79,9 @@ record Day where The default `MkDay` constructor is slightly cumbersome to use, always requiring _something_ for the `part2` slot, even if there isn't a part 2 yet, and -requiring that `part2` be wrapped in a `Just` when there is one, so we provide a -pair of constructors for the case where there is only a `part1` and for where -there is a `part1` and a `part2` that handle that for us. +requiring that `part2` be wrapped in a `Just` when there is one. We provide a +pair of constructors for the case where there is only a `part1`, as well as one +for when there is a `part1` and a `part2`. ```idris namespace Day @@ -91,8 +90,7 @@ namespace Day ### First The `First` constructor only accepts a `part1`, it does the work of filling in -`part2` with `Nothing` and setting all of `part2`'s type arguments to `()` for -us.' +`part2` with `Nothing` and setting all of `part2`'s type arguments to `()`. ```idris ||| Constructor for a day with only part one ready to run @@ -106,8 +104,8 @@ us.' ### Both -The `Both` constructor does a little bit less heavy lifting, the only thing it -needs to do for us is wrap `part2` in a `Just`. +The `Both` constructor does less heavy lifting, the only thing it needs to do is +wrap `part2` in a `Just`. ```idris ||| Constructor for a day with both parts ready to run @@ -123,16 +121,17 @@ needs to do for us is wrap `part2` in a `Just`. ## Freshness We will be using a _Fresh List_ from the -[structures](https://git.sr.ht/~thatonelutenist/Structures) package to build -defensiveness into the API. A Fresh List structurally only allows you to prepend -an element onto it when it satisfies some _freshness_ criteria relative to the -elements already in the list. +[structures](https://git.sr.ht/~thatonelutenist/Structures) package to build our +API defensively against duplicate days and cosmetically annoying out of order +day registration. A Fresh List structurally only allows you to prepend/cons an +element onto it when it satisfies some _freshness criteria_ relative to the +elements already contained in the list. -Here, we compare the day numbers of the two `Day`s using the less-than +We compare the day numbers of the two `Day`s using the less-than(`<`) relationship. Since we are operating on the start of the list when this comparison takes place, this enforces, through type checking, that the resulting -Fresh List is sorted in ascending order and that no two `Day`s have the same day -number. +Fresh List of `Day`s is sorted in ascending order and that no two `Day`s have +the same day number. ```idris ||| Freshness criteria for days @@ -150,7 +149,7 @@ FreshDay x y = x.day < y.day # The `Year` Record The `Year` record collects a number of `Day`s into a single Fresh List for the -year, and is mostly just a simple container. +year, also containing the year number for this collection. ```idris ||| Collect all the days in a given year @@ -166,9 +165,10 @@ record Year where Much like `Day`s are stored in a `FreshList` in `Year`, `Year`s will be stored in a `FreshList` in `Advent`, so we need to provide a freshness criteria for -`Year` as well. We do so by applying the less-than relationship against the year -number of the two `Years`, for the same reasons and with the same results as -with `FreshDay`. +`Year` as well. + +We do so by applying the less-than relationship against the year number of the +two `Years`, for the same reasons and with the same results as with `FreshDay`. ```idris ||| Freshness criteria for years @@ -186,8 +186,7 @@ FreshYear x y = x.year < y.year # The `Advent` Record The `Advent` record collects a number of `Year`s in much the same way that -`Year` collects a number of days, sorting the `Year`s in a `FreshList` to -provide API defensiveness. +`Year` collects a number of days. ```idris ||| Collect all years diff --git a/src/Util/Eff.md b/src/Util/Eff.md index 1b51cba..1baa453 100644 --- a/src/Util/Eff.md +++ b/src/Util/Eff.md @@ -22,9 +22,18 @@ import System.File Basic enumeration describing log levels, we define some (hidden) utility functions for working with these. +The `Other n` log level is restricted to `n` greater than 4, to prevent +ambiguity between custom log levels and predefined log levels. + ```idris public export -data Level = Err | Warn | Info | Debug | Trace | Other Nat +data Level : Type where + Err : Level + Warn : Level + Info : Level + Debug : Level + Trace : Level + Other : (n : Nat) -> {auto _ : n `GT` 4} -> Level ``` # Days @@ -87,6 +88,12 @@ y2015 = MkYear 2015 [ , day10 ``` +## [Day 11](Y2015/Day11.md) + +```idris + , day11 +``` + ```idris ] ``` diff --git a/src/Years/Y2015/Day1.md b/src/Years/Y2015/Day1.md index cfc4950..f8820d3 100644 --- a/src/Years/Y2015/Day1.md +++ b/src/Years/Y2015/Day1.md @@ -1,4 +1,4 @@ -# Year 2015 Day 1 +# [Year 2015 Day 1](https://adventofcode.com/2015/day/1) Pretty simple, basic warmup problem, nothing really novel is on display here except the effectful part computations. diff --git a/src/Years/Y2015/Day10.md b/src/Years/Y2015/Day10.md index 7971126..201e0c5 100644 --- a/src/Years/Y2015/Day10.md +++ b/src/Years/Y2015/Day10.md @@ -1,4 +1,4 @@ -# Year 2015 Day 10 +# [Year 2015 Day 10](https://adventofcode.com/2015/day/10) This day doesn't really add anything new, but we will show off our new views for viewing integers as lists of digits. diff --git a/src/Years/Y2015/Day11.md b/src/Years/Y2015/Day11.md new file mode 100644 index 0000000..0f6ccc6 --- /dev/null +++ b/src/Years/Y2015/Day11.md @@ -0,0 +1,227 @@ +# [Year 2015 Day 11](https://adventofcode.com/2015/day/11) + +This day provides a gentle introduction to refinement types, types which augment +other types with a predicate that must hold for all the values of the refined +type, which allow easily defining types as subsets of other types based on some +property of the acceptable elements. + +While refinement types are quite easy to implement in Idris, and we easily could +implement the one we need for today's task as a throw away data structure just +for this module, we will be using the `refined`[^1] library's implementation for +the sake of getting on with it. + + + +```idris +import Data.Vect +import Data.String +import Data.Refined.Char + +import Util +``` + +## Data Structures and Parsing + +Provide a predicate which establishes that a char is a lowercase alphabetic +character, the only type of character that passwords are allowed to contain. We +use the `FromTo` predicate from the `refined`[^1] library to restrict chars to +within the range from `a` to `z`. + +This predicate has multiplicity 0, a full discussion of multiplicites and linear +types is out of scope for today, but put simply this enforces that a value of +this predicate type can be "used" at most 0 times, having the effect of erasing +the value at runtime, making this more or less a zero-cost abstraction. + +```idris +0 IsPasswordChar : Char -> Type +IsPasswordChar = FromTo 'a' 'z' +``` + +Combine a `Char` with its corresponding `IsPasswordChar` predicate into a +combined "refined" type, whose elements are the subset of `Char`s that are +lowercase alphabetic characters. + +```idris +record PasswordChar where + constructor MkPC + char : Char + {auto 0 prf : IsPasswordChar char} +%name PasswordChar pc +``` + + + +A function to fallible convert `Char`s into refined `PasswordChar`s, this will +return `Just` if the `Char` satisfies the predicate, and `Nothing` otherwise, +aligning with the type-level guarantees of the `PasswordChar` type. + +```idris +refineChar : Char -> Maybe PasswordChar +refineChar c = map fromSubset $ refine0 c + where + fromSubset : Subset Char IsPasswordChar -> PasswordChar + fromSubset (Element char prf) = MkPC char +``` + +Convenience function returning `a` as a `PasswordChar` + +```idris +lowest : PasswordChar +lowest = MkPC 'a' +``` + +"Increment" a `PasswordChar`, changing it to the next letter (`a` becomes `b`, +`b` becomes `c`, so on), returning nothing if we go past `z`, corresponding to a +carry. + +We do this by converting the internal `Char` to an integer, adding one to it, +then converting back to a `Char`. This low-level conversion loses the refinement +context, forcing us to call `refineChar` on the new value to bring it back into +the refined type, providing us type-level assurance that this function will +return `Nothing` if an overflow occurs. + +```idris +incriment : PasswordChar -> Maybe PasswordChar +incriment (MkPC char) = + let next = chr $ ord char + 1 + in refineChar next +``` + +A `Password` is a `Vect` of 8 `PasswordChar`s. This `Vect` is sorted in reverse +order compared to the `String` it corresponds to, with the right-most letter +first, to make implementing the `incrimentPassword` function a little easier and +cleaner. + +We also provide conversion to/from a `String` + +```idris +Password : Type +Password = Vect 8 PasswordChar + +parsePassword : Has (Except String) fs => String -> Eff fs Password +parsePassword str = do + cs <- note "Password has incorrect number of characters: \{str}" + . toVect 8 . reverse . unpack $ str + cs <- note "Password contained invalid characters: \{str}" + $ traverse refineChar cs + pure cs + +passwordToString : Password -> String +passwordToString = pack . toList . reverse . map char +``` + +Define a function to increment a `Password`, this function will "roll over", +producing `aaaaaaaa` if provided `zzzzzzzz`. + +```idris +incrimentPassword : Vect n PasswordChar -> Vect n PasswordChar +incrimentPassword [] = [] +incrimentPassword (x :: xs) = + case incriment x of + Nothing => lowest :: incrimentPassword xs + Just x => x :: xs +``` + +### Password validity + +A password must contain a run of at least 3 incrementing characters, check this +by converting the `PasswordChar`s to their integer representations. Remember +that our `Password` `Vect` is backwards compared to the string representation. + +```idris +incrimentingChars : Vect n PasswordChar -> Bool +incrimentingChars (z :: next@(y :: (x :: xs))) = + let [x, y, z] : Vect _ Int = map (ord . char) [x, y, z] + in if y == x + 1 && z == y + 1 + then True + else incrimentingChars next +incrimentingChars _ = False +``` + +A password may not contain `i`, `o`, or `l` + +```idris +noInvalidChars : Vect n PasswordChar -> Bool +noInvalidChars = not . (any (flip contains $ ['i', 'o', 'l'])) . map char +``` + +A password contains at least two different non-overlapping pairs. + +We check this by pattern matching our password two characters at a time, +consuming both characters if a matched pair is found, and tacking on the `Char` +the list is composed of to an accumulator list as we go. This list is then +reduced to only its unique elements (it's `nub`), and checking to see if it's +length is at least 2. + +```idris +containsPairs : Vect n PasswordChar -> Bool +containsPairs xs = length (nub $ pairs (reverse xs) []) >= 2 + where + pairs : Vect m PasswordChar -> (acc : List Char) -> List Char + pairs [] acc = acc + pairs (x :: []) acc = acc + pairs (x :: (y :: xs)) acc = + if x == y + -- If there is a pair, consume it to prevent detecting overlapping pairs + then pairs xs (x.char :: acc) + -- If there isn't a pair, only consume one character + else pairs (y :: xs) acc +``` + +Combine our password criteria into one function + +```idris +part1Critera : Vect n PasswordChar -> Bool +part1Critera xs = incrimentingChars xs && noInvalidChars xs && containsPairs xs +``` + +### Find the next password + +Find the next password based on a criteria function + +```idris +findNextPassword : + (f : Vect n PasswordChar -> Bool) -> (password : Vect n PasswordChar) + -> Vect n PasswordChar +findNextPassword f password = + let next = incrimentPassword password + in if f next + then next + else findNextPassword f next +``` + +## Part Functions + +### Part 1 + +```idris +part1 : Eff (PartEff String) (String, ()) +part1 = do + input <- map trim $ askAt "input" + password <- parsePassword input + info "Starting password: \{show password} -> \{passwordToString password}" + let next_password = findNextPassword part1Critera password + pure (passwordToString next_password, ()) +``` + + + +## References + +[^1]: https://github.com/stefan-hoeck/idris2-refined/ diff --git a/src/Years/Y2015/Day2.md b/src/Years/Y2015/Day2.md index 43ca0b1..22081b2 100644 --- a/src/Years/Y2015/Day2.md +++ b/src/Years/Y2015/Day2.md @@ -1,4 +1,4 @@ -# Year 2015 Day 2 +# [Year 2015 Day 2](https://adventofcode.com/2015/day/2) This day provides us our first little taste of effectful parsing diff --git a/src/Years/Y2015/Day3.md b/src/Years/Y2015/Day3.md index 9dd7ecc..195d1d9 100644 --- a/src/Years/Y2015/Day3.md +++ b/src/Years/Y2015/Day3.md @@ -1,4 +1,4 @@ -# Year 2015 Day 3 +# [Year 2015 Day 3](https://adventofcode.com/2015/day/3) This day provides a gentle introduction to `mutual` blocks and mutually recursive functions. diff --git a/src/Years/Y2015/Day4.md b/src/Years/Y2015/Day4.md index a1fee57..f907fa1 100644 --- a/src/Years/Y2015/Day4.md +++ b/src/Years/Y2015/Day4.md @@ -1,4 +1,4 @@ -# Year 2015 Day 4 +# [Year 2015 Day 4](https://adventofcode.com/2015/day/4) This day introduces us to a little bit of FFI, linking to openssl to use it's `MD5` functionality. diff --git a/src/Years/Y2015/Day5.md b/src/Years/Y2015/Day5.md index d947885..e41bd96 100644 --- a/src/Years/Y2015/Day5.md +++ b/src/Years/Y2015/Day5.md @@ -1,4 +1,4 @@ -# Year 2015 Day 5 +# [Year 2015 Day 5](https://adventofcode.com/2015/day/5) This day provides a nice chance to introduce [views](https://idris2.readthedocs.io/en/latest/tutorial/views.html), diff --git a/src/Years/Y2015/Day6.md b/src/Years/Y2015/Day6.md index a2b5cd0..131be48 100644 --- a/src/Years/Y2015/Day6.md +++ b/src/Years/Y2015/Day6.md @@ -1,4 +1,8 @@ -# Year 2015 Day 6 +# \[Year 2015 Day 6\](https://adventofcode.com/2015/day/ + +6. + +Introduction to the advent of code classic 2d grid problem.