Add dot-dsl exercise

[ageron]

This one did not have any test cases in the problem specs, so I had very little guidance.

The goal of the exercise is to implement a DSL that looks like the Dot format:

    graph {
        graph [bgcolor="yellow"]
        a [color="red"]
        b [color="blue"]
        a -- b [color="green"]
    }

The DSL I came up with looks close enough:

    graph = buildGraph { bgColor: Yellow } [
        node "a" { color: Red },
        node "b" { color: Blue },
        edge "a" "b" { color: Green },
    ]

However, I feel like the fun and interesting part was designing this DSL. Now the users just need to implement the buildGraph function that reads the DSL commands and builds a graph: it's okay, but not super interesting, IMHO. Perhaps it's enough to get the users familiar with the idea of a DSL and how to build one in Roc.

Another option would be to make the tests agnostic to the DSL itself, as long as it can build the right graphs. For example:

import DotDsl exposing [buildGraph, dslCommandsForGraph1, dslCommandsForGraph2, ...]
expect
    result = dslCommandsForGraph1 |> buildGraph
    expected = { bgColor: ..., nodes: ..., edges: ...} # graph 1
    result == expected

expect
    result = dslCommandsForGraph2 |> buildGraph
    expected = { bgColor: ..., nodes: ..., edges: ...} # graph 2
    result == expected

...

This way the user gets to come up with their own DSL, which is the interesting part, and they also get to use it to build a few graphs. But perhaps this does not give users enough guidance. They could just define dslCommandsForGraph1 to be equal to the expected graph 1, and make buildGraph the identity function, it wouldn't be very interesting. Or perhaps we can guide them a little bit in the docs, by suggesting a DSL like the one I designed. I'm not sure, WDYT?

Note: if we stick to the current approach, perhaps I can add a test that requires the user to use the DSL to build a specific graph? For example:

# use the DSL to create this test graph
expect
    result = dslCommandsForTestGraph |> buildGraph
    expected = { bgColor: ..., nodes: ..., edges: ...} # test graph
    result == expected

[isaacvando]

I like the idea of having the students come up with the DSL themselves! I agree that that is the most fun part.

[ageron]

Sounds good, I'll update the exercise then, thanks for your feedback, Isaac.