Friday, August 28, 2020

Sudoku Visualization

The Sudoku solver visualization in Elm is done!

Writing Elm feels similar to writing Haskell, with a bit of syntax that's more like F# (e.g. the pipeline operators <| and |>). Between the familiar format of Learn You and Elm and the examples in Beginning Elm, it's relatively easy to pick up given a bit of functional programming background.

All of the code for the solver and visualization is on GitHub.


Wednesday, August 26, 2020

Elm JSON Decoder

In the vein of functional programming, I've been learning Elm to visualize the progress of a Sudoku solver.

The JSON decoding tutorials are clear, and the JSON.Decode library is well-documented once you know how to read it (in general, the library documentation in Elm seems to be on the terse side). 

Two things were not very clear from initial read of the docs: how to parse lists to tuples, and how to parse strings to custom types. 

Leaning on SO for the below example,  tuples apparently used to be supported as first-class decoders, but in the current version of Json.Decoder, index seems to be the official way to construct decoders for tuples. 

arrayAsTuple2 a b c =

    Decode.index 0 a

        |> Decode.andThen (\ aVal -> Decode.index 1 b

            |> Decode.andThen (\ bVal -> Decode.succeed (aVal, bVal)))            

boardDecoder : Decoder Board

boardDecoder = Decode.list <| arrayAsTuple2 

Elm 0.19 only supports up to three-value tuples (somewhat surprising coming from Haskell, though with records and custom data types, the decision to limit unnamed tuples has a certain logic...). So the helper construction isn't too bad.

Parsing strings to custom data types turns out to be more straightforward, though a bit repetitive (especially if you need to later get the string representation back out of custom data type -- there is no deriving Show in Elm). First decode the string, then chain a pattern match using andThen:

data Transform = Rows | Cols | Boxes

transformDecoder : Decoder Transform
transformDecoder =
    |> Decode.andThen
       (\ s ->
            case s of
                "Rows" -> Decode.succeed Rows
                "Cols" -> Decode.succeed Cols
                "Boxes" -> Decode.succeed Boxes
                _ -> <| "Unknown transformation.")

Saturday, August 22, 2020

Recurse Center

 I've wanted to attend the Recurse Center (formerly known as Hacker School) or a while, and have finally found the time to do so. It's very consistent with the free education path (it's free!), and so far has been a great source of exposure to new topics and ideas, as well as of inspiration to work on different classes of problems. They've put a lot of effort into fostering a healthy, supportive community, and the nature of the program is such that self-motivated, inquisitive learners more or less self-select themeselves into attendance. Some topics I was exposed to or participated in so far -- audio programming, gaming, lower-level / systems programming languages (eg Zig), functional programming (eg Haskell, Elm), procedural generetion, Web Assembly compilation... There are folks of all walks of life, skills, and interests in the community, making it something that I expect will continue to yield rich experiences for the remainder of the three-month batch.