doc: Literate Main

src/Main.md

@@ -1,5 +1,14 @@
-module Main
+# Advent of Code
 
+This module provides a command line interface for running the solution to a specific day for a specific year, run as `advent $YEAR $DAY`. 
+
+This runner will automatically locate the appropriate input file and then run the selected day's solution against it. See [Runner](Runner.md) for the definitions of the `Day`, `Year`, and `Advent` data types.
+
+```idris
+module Main
+```
+
+<!-- idris 
 import System
 import System.Path
 import System.File
@@ -10,7 +19,9 @@ import Data.Vect
 
 import Control.Eff
 import Derive.Prelude
+-->
 
+```idris
 import Structures.Dependent.FreshList
 
 import Runner
@@ -21,15 +32,16 @@ import Years.Y2015;
 
 %language ElabReflection
 %default total
+```
 
+# Command Line Interface
+
+Since this is a simple application, I am using `GetOpt` from `contrib` for argument parsing. Here we define our options list, a data type to describe our flags, and the usage message header.
+
+```idris
 data Flag = UseExample | Verbose
 %runElab derive "Flag" [Eq, Show]
 
-advent : Advent
-advent = MkAdvent [
-    y2015
-  ]
-
 options : List (OptDescr Flag)
 options =
   [
@@ -39,7 +51,13 @@ options =
 
 header : String
 header = "Usage: advent YEAR DAY [OPTION...]"
+```
 
+## Error Type
+
+We will be using one unified error type for the entire `Main` module, but we must go ahead and define it before we go any further with command line arguments parsing, as we are about to do some things that might fail.
+
+```idris
 data Error : Type where
   OptionsError : (errs : List String) -> Error
   ArgumentsError : (count : Nat) -> Error
@@ -50,7 +68,12 @@ data Error : Type where
   InputRead : (path : String) -> (err : FileError) -> Error
   SolveError : Show e => (year, day, part : Nat) -> (err : e) -> Error
 %name Error err
+```
 
+A `Show` implementation for `Error` is provided, hidden in this document for brevity.
+
+
+<!-- idris
 Show Error where
   show (OptionsError errs) =
     let errs = unlines . map ("  " ++) . lines . joinBy "\n" $ errs
@@ -72,7 +95,13 @@ Show Error where
   show (SolveError year day part err) =
     let err = unlines . map ("  " ++) . lines . show $ err
     in "Error solving day \{show day} part \{show part} of year \{show year}: \n" ++ err
+-->
 
+## Extract the year and day
+
+After peeling off our options from the arguments using `GetOpt`, we will be left with a list of non-option arguments, which we must then parse into our year number/day number pair. We perform some pattern matching to make sure the list is the correct length, and then parse the individual integers, throwing an error if anything goes wrong
+
+```idris
 ||| Convert the non-option arguments into a Year/Day pair
 argumentsToPair : Has (Except Error) fs =>
   List String -> Eff fs (Nat, Nat)
@@ -83,17 +112,57 @@ argumentsToPair [year, day] = do
   day <- note (InvalidDay year day) $ parsePositive day
   pure (year, day)
 argumentsToPair xs = throw $ ArgumentsError (length xs)
+```
 
+# The Advent 
+
+Construct our top-level `Advent` record from the imported `Year` modules. The argument to the `MkAdvent` constructor is a `FreshList`, with a freshness criteria ensuring that the list is in ascending order and does not include any duplicate `Year`s.
+
+```idris
+advent : Advent
+advent = MkAdvent [
+    y2015
+  ]
+```
+
+# The Hard Part
+
+Now we must glue everything together, parse our arguments, handle any supplied options, locate the relevant year and day, locate the corresponding input file, read it, and then run the selected `Day` against it.
+
+Because we are building our application around effects, the actual core of the application is the effectful `start` computation, that the `main` function will then apply `IO` based handlers to.
+
+Our reader and writer aren't ready yet, we need to do some setup first, so the top level type signature doesn't include them, so we'll add them to the effects list as they become available.
+
+```idris
 covering
 ||| Actual main, as an effectful computation
 start : Eff [IO, Except Error] ()
 start = do
+```
+
+## Parsing the arguments
+
+Feed the augments from `System.getArgs` into `getOpt`, making sure to drop the name the binary was invoked with, then check for any errors in the result, throwing our own error if any are encountered.
+
+```idris
   -- Read and parse arguments/options
   args <- getArgs
   let opts = getOpt Permute options (drop 1 args)
   when (not . null $ opts.errors) $
     throw (OptionsError opts.errors)
+```
+
+Use our `argumentsToPair` function to extract the selected year and day numbers from the positional arguments, implicitly throwing an error if there are any failures doing so.
+
+```idris
   (year, day_n) <- argumentsToPair opts.nonOptions
+```
+
+## 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.
+
+```idris
   -- If the verbose flag is set, hook up the logging writer to stderr
   let verbose = any (== Verbose) opts.options
   let logHandler : Eff [IO, Except Error, WriterL "log" String] () -> Eff [IO, Except Error] () =
@@ -102,6 +171,13 @@ start = do
        else handleLog (\x => pure ())
   -- Add the logging writer to the effect
   logHandler $ do
+```
+
+Find the current directory and append to it to find the input file. If the `--use-example/-u` flag is set, look for the input file at `inputs/examples/$year/$day`, otherwise look for it at `inputs/real/$year/$day`.
+
+After we've located it, attempt to read from it, throwing an `InputRead` error if any errors occur, then insert the contents into our `Reader` and inject it into the effects list.
+
+```idris
   -- Locate and read in the input file
   Just cwd <- currentDir | _ => throw NoCurrentDir
   let cwd = parse cwd
@@ -112,13 +188,30 @@ start = do
   Right contents <- readFile input_path | Left err => throw $ InputRead input_path err
   -- Now add the reader that provides the input to the effect
   runReaderAt "input" contents {fs = PartEff Error} $ do
+```
+
+Try and locate the `Day` in our `Advent` record, throwing an error if we are unable to locate it
+
+```idris
   -- Attempt to locate the provided day
   Just day <- pure $ locate year day_n advent | _ => throw $ NoSuchDay year day_n
+```
+
+## Executing the parts
+
+Run the selected `Day`'s part 1, wrapping any errors that it returns in a `SolveError`. Collect both the result and the opaque context value, then print out the result.
+
+```idris
   -- Run part 1
   part_1 <- lift $ runExcept day.part1
   (part_1, ctx) <- rethrow . mapLeft (SolveError year day_n 1 @{day.showErr1}) $ part_1
   putStrLn "\{show year} day \{show day_n} part 1:"
   putStrLn $ unlines . map ("  " ++) . lines . show @{day.showOut1} $ part_1
+```
+
+Check and see if the selected `Day` has a part 2, if it does, feed the opaque context value collected from part 1 into it, wrap any errors that it returns in a `SolveError`, then print out the result, then return, closing out the program.
+
+```idris
   -- Run part 2 if we have it
   case day.part2 of
     Nothing => pure ()
@@ -127,15 +220,41 @@ start = do
       part_2 <- rethrow . mapLeft (SolveError year day_n 2 @{day.showErr2}) $ part_2
       putStrLn "\{show year} day \{show day_n} part 2:"
       putStrLn $ unlines . map ("  " ++) . lines . show @{day.showOut2} $ part_2
+```
+
+## Helper functions
+
+```idris
   where
+```
+
+### Print strings to stderr
+
+Putting this in its own function makes dealing with the potential error returned by `fPutStrLn` a bit eaiser. It's reasonable to ignore this error, since if we can't write to stderr we are kinda powerless to tell anyone about it.
+
+```idris
     -- print to standard error
     ePutStrLn : String -> IO ()
     ePutStrLn str = do
       _ <- fPutStrLn stderr str
       pure ()
+```
+
+### Decompose a Writer
+
+Having this be a function keeps the `a` somewhat opaque and helps with they type checking. Only values of `Writer $TYPE ()` can actually be constructed, but the type checker gets a little bit confused about this when you try to do this by pattern matching inline.
+
+```idris
     -- Decompose a writer, eases type inference
     unwriter : WriterL "log" String a -> (a, String)
     unwriter (Tell vw) = ((), vw)
+```
+
+### 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. 
+
+```idris
     -- Lowers logging into IO within the effect using the given IO function
     handleLog :
       Has (WriterL "log" String) fs => Has IO (fs - WriterL "log" String) => 
@@ -146,7 +265,15 @@ start = do
             do let (val, msg) = unwriter msg
                _ <- send $ tell msg
                f val) x
+```
 
+# Handle the effectful action as an IO action 
+
+Use `runEff` to translate the effects in `start`'s effects list into IO actions, and return the resulting `IO ()`.
+
+The `IO` component of the effects list is handled via `id`, translating `IO` actions into themselves, and we construct a helper function to handle errors as IO actions by printing the error and crashing the program.
+
+```idris
 covering
 ||| Shim main, which simply executes the effectful computation
 main : IO ()
@@ -156,3 +283,4 @@ main = runEff start [id, handleError]
   handleError (Err err) = do
     printLn err
     exitFailure
+```

src/Runner.idr

@@ -1,88 +0,0 @@
-module Runner
-
-import Control.Eff
-import Structures.Dependent.FreshList
-
-||| The effect type is the same in boths parts one and two, modulo potentially
-||| different error types, so we calucate it here
-public export
-PartEff : (err : Type) -> List (Type -> Type)
-PartEff err =
-  [IO, Except err, WriterL "log" String, ReaderL "input" String]
-
-||| Model solving a single day
-public export
-record Day where
-  constructor MkDay
-  day : Nat
-  {0 out1, out2, err1, err2 : Type}
-  {auto showOut1 : Show out1}
-  {auto showOut2 : Show out2}
-  {auto showErr1 : Show err1}
-  {auto showErr2 : Show err2}
-  part1 : Eff (PartEff err1) (out1, ctx)
-  part2 : Maybe (ctx -> Eff (PartEff err2) out2)
-%name Day day, day2, day3
-
-namespace Day
-  ||| Constructor for a day with only part one ready to run
-  public export
-  First : Show err => Show out =>
-    (day : Nat) -> (part1 : Eff (PartEff err) (out, ctx'))
-    -> Day
-  First day part1 =
-    MkDay day part1 Nothing {out2 = ()} {err2 = ()}
-
-  ||| Constructor for a day with both parts ready to run
-  public export
-  Both : Show o1 => Show o2 => Show e1 => Show e2 =>
-    (day : Nat) -> (part1 : Eff (PartEff e1) (o1, ctx')) ->
-    (part2 :ctx' -> Eff (PartEff e2) o2)
-    -> Day
-  Both day part1 part2 =
-    MkDay day part1 (Just part2)
-
-||| Freshness criteria for days
-|||
-||| A day is fresh compared to another if the day number of the former day is
-||| strictly less than the day number of the latter day
-|||
-||| This ensures that the days list is always in incrimenting sorted order
-||| (since we are consing to the front of the list) with no duplicate days
-public export
-FreshDay : Day -> Day -> Bool
-FreshDay x y = x.day < y.day
-
-||| Collect all the days in a given year
-public export
-record Year where
-  constructor MkYear
-  year : Nat
-  days : FreshList FreshDay Day
-%name Year year, year2, year3
-
-||| Freshness criteria for years
-|||
-||| A year is fresh compared to another if the year number of the former year is
-||| strictly less than the year number of the latter year
-|||
-||| This ensures that the years list is always in incrimenting sorted order
-||| (since we are consing to the front of the list) with no duplicate years
-public export
-FreshYear : Year -> Year -> Bool
-FreshYear x y = x.year < y.year
-
-||| Collect all years
-public export
-record Advent where
-  constructor MkAdvent
-  years : FreshList FreshYear Year
-%name Advent advent, advent2, advent3
-
-namespace Advent
-  ||| Attempt to locate `Day` entry corresponding to the provided day and year numbers
-  export
-  locate : (year, day : Nat) -> Advent -> Maybe Day
-  locate year day advent = do
-    year <- find (\x => x.year == year) advent.years
-    find (\x => x.day == day) year.days

src/Runner.md

@@ -0,0 +1,174 @@
+# Unified interface for any day from any year
+
+This module provides some basic data types for building an application containing all my solutions to all of the parts of all the days across all of the years.
+
+This provides a defensively built API for constructing the overall `Advent` data structure that prevents registering a day/year twice or registering days/years out of order. 
+
+```idris
+module Runner
+
+import Control.Eff
+import Structures.Dependent.FreshList
+
+%default total
+```
+
+# 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.
+
+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 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 reasons.
+
+```idris
+||| The effect type is the same in boths parts one and two, modulo potentially
+||| different error types, so we calucate it here
+public export
+PartEff : (err : Type) -> List (Type -> Type)
+PartEff err =
+  [IO, Except err, WriterL "log" String, ReaderL "input" String]
+```
+
+# 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.
+
+`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 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`.
+
+```idris
+||| Model solving a single day
+public export
+record Day where
+  constructor MkDay
+  day : Nat
+  {0 out1, out2, err1, err2 : Type}
+  {auto showOut1 : Show out1}
+  {auto showOut2 : Show out2}
+  {auto showErr1 : Show err1}
+  {auto showErr2 : Show err2}
+  part1 : Eff (PartEff err1) (out1, ctx)
+  part2 : Maybe (ctx -> Eff (PartEff err2) out2)
+%name Day day, day2, day3
+```
+
+## Smarter Constructors
+
+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.
+
+```idris
+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.'
+
+```idris
+  ||| Constructor for a day with only part one ready to run
+  public export
+  First : Show err => Show out =>
+    (day : Nat) -> (part1 : Eff (PartEff err) (out, ctx'))
+    -> Day
+  First day part1 =
+    MkDay day part1 Nothing {out2 = ()} {err2 = ()}
+```
+
+### 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`.
+
+```idris
+  ||| Constructor for a day with both parts ready to run
+  public export
+  Both : Show o1 => Show o2 => Show e1 => Show e2 =>
+    (day : Nat) -> (part1 : Eff (PartEff e1) (o1, ctx')) ->
+    (part2 :ctx' -> Eff (PartEff e2) o2)
+    -> Day
+  Both day part1 part2 =
+    MkDay day part1 (Just part2)
+```
+
+## 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.
+
+Here, 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.
+
+```idris
+||| Freshness criteria for days
+|||
+||| A day is fresh compared to another if the day number of the former day is
+||| strictly less than the day number of the latter day
+|||
+||| This ensures that the days list is always in incrimenting sorted order
+||| (since we are consing to the front of the list) with no duplicate days
+public export
+FreshDay : Day -> Day -> Bool
+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.
+
+```idris
+||| Collect all the days in a given year
+public export
+record Year where
+  constructor MkYear
+  year : Nat
+  days : FreshList FreshDay Day
+%name Year year, year2, year3
+```
+
+## Freshness
+
+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`.
+
+```idris
+||| Freshness criteria for years
+|||
+||| A year is fresh compared to another if the year number of the former year is
+||| strictly less than the year number of the latter year
+|||
+||| This ensures that the years list is always in incrimenting sorted order
+||| (since we are consing to the front of the list) with no duplicate years
+public export
+FreshYear : Year -> Year -> Bool
+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.
+
+```idris
+||| Collect all years
+public export
+record Advent where
+  constructor MkAdvent
+  years : FreshList FreshYear Year
+%name Advent advent, advent2, advent3
+```
+
+## Methods
+
+```idris
+namespace Advent
+```
+
+### locate
+
+This is a utility function that searches the `FreshList` of `Year`s for the provided year number, then searches the resulting `Year`, if one exists, for the provided day number.
+
+We don't have to worry about potentially encountering duplicates here because of the freshness restriction. 
+
+```idris
+  ||| Attempt to locate `Day` entry corresponding to the provided day and year numbers
+  export
+  locate : (year, day : Nat) -> Advent -> Maybe Day
+  locate year day advent = do
+    year <- find (\x => x.year == year) advent.years
+    find (\x => x.day == day) year.days
+```