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Revise Runner

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Nathan McCarty 2025-01-23 00:29:53 -05:00
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src/Runner.md
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@ -22,16 +22,15 @@ import public Util.Eff
# Effectful Parts # Effectful Parts
The solution to each part of a day is run as an effectful computation, and as 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 the effect stack is meant to be the same across both parts, only varying in the
in the type of the error value in the `Except` effect, I construct a type level type of the error value for the `Except` effect, we construct a type level
function to have a single source of truth for this. The `err` type can be any function to have a single source of truth. The `err` type can be any type with a
type with a `Show` implementation, but that constraint will be tacked on in the `Show` implementation, but that constraint will be tacked on in the next step.
next step.
The `Logger` effect is provided for logging, and a `Reader` effect is provided The `Logger` 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` to pass in the input, to make the top level API a little bit cleaner. `IO` is
is also provided, even though the part solutions themselves shouldn't really be 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. reasons.
```idris ```idris
@ -46,19 +45,19 @@ PartEff err =
# The `Day` Record # The `Day` Record
The `Day` type groups together an effectful `part1` computation, an optional The `Day` type groups together an effectful `part1` computation, an optional
effectful `part2` computation, the day number, and does some type wrangling to effectful `part2` computation, and the day number, with some type wrangling to
get the type system out of our way on this one. get the type system out of our way.
`part1` and `part2` are allowed independent output and error types, and this `part1` and `part2` are allowed independent output and error types, and this
record captures `Show` implementations for those output and error types so that 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. actually know what the types are.
It is often useful to pass a bit of context, such as the data structures 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 resulting from parsing, between `part1` and `part2`. This is achieved through
erased `ctx` type, which is totally opaque here. The runner code in `Main` will the erased `ctx` type, which is totally opaque to the runner. The code in `Main`
provide the value of the `ctx` type produced as part of the output of `part1` as will provide the value of the `ctx` type produced as part of the output of
the input of `part2`. `part1` and as the input of `part2`.
```idris ```idris
||| Model solving a single day ||| Model solving a single day
@ -80,9 +79,9 @@ record Day where
The default `MkDay` constructor is slightly cumbersome to use, always requiring 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 _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 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` and for where pair of constructors for the case where there is only a `part1`, as well as one
there is a `part1` and a `part2` that handle that for us. for when there is a `part1` and a `part2`.
```idris ```idris
namespace Day namespace Day
@ -91,8 +90,7 @@ namespace Day
### First ### First
The `First` constructor only accepts a `part1`, it does the work of filling in 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 `part2` with `Nothing` and setting all of `part2`'s type arguments to `()`.
us.'
```idris ```idris
||| Constructor for a day with only part one ready to run ||| Constructor for a day with only part one ready to run
@ -106,8 +104,8 @@ us.'
### Both ### Both
The `Both` constructor does a little bit less heavy lifting, the only thing it The `Both` constructor does less heavy lifting, the only thing it needs to do is
needs to do for us is wrap `part2` in a `Just`. wrap `part2` in a `Just`.
```idris ```idris
||| Constructor for a day with both parts ready to run ||| 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 ## Freshness
We will be using a _Fresh List_ from the We will be using a _Fresh List_ from the
[structures](https://git.sr.ht/~thatonelutenist/Structures) package to build [structures](https://git.sr.ht/~thatonelutenist/Structures) package to build our
defensiveness into the API. A Fresh List structurally only allows you to prepend API defensively against duplicate days and cosmetically annoying out of order
an element onto it when it satisfies some _freshness_ criteria relative to the day registration. A Fresh List structurally only allows you to prepend/cons an
elements already in the list. 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 relationship. Since we are operating on the start of the list when this
comparison takes place, this enforces, through type checking, that the resulting 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 Fresh List of `Day`s is sorted in ascending order and that no two `Day`s have
number. the same day number.
```idris ```idris
||| Freshness criteria for days ||| Freshness criteria for days
@ -150,7 +149,7 @@ FreshDay x y = x.day < y.day
# The `Year` Record # The `Year` Record
The `Year` record collects a number of `Day`s into a single Fresh List for the 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 ```idris
||| Collect all the days in a given year ||| 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 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 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 `Year` as well.
number of the two `Years`, for the same reasons and with the same results as
with `FreshDay`. 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 ```idris
||| Freshness criteria for years ||| Freshness criteria for years
@ -186,8 +186,7 @@ FreshYear x y = x.year < y.year
# The `Advent` Record # The `Advent` Record
The `Advent` record collects a number of `Year`s in much the same way that 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 `Year` collects a number of days.
provide API defensiveness.
```idris ```idris
||| Collect all years ||| Collect all years