[New practice exercise] Line Up

[colinleach]

I'm doing some easier stuff at the moment (see below for more details).

This is a recently-added exercise on string interpolation and logic. I just used multiple if () return() statements, but a switch should also work.

Difficulty 1 copies Python, and seems reasonable. Other tracks have a scattering of 2's and 3's.

[colinleach]

I wrote this mid-June:

I hope to PR the occasional draft concept, but nothing that needs urgent review.

Didn't happen. I seemed to go through a period of broad-spectrum uselessness, and did very little (just some tinkering with cross-track dataframe stuff).

Then I thought about getting back into it with some new practice exercises: relatively easy, and gives the new test generators a workout.

Then I went off track and decided the Fortran track looks a bit thin. Details on the forum. TL;DR, Isaac and Andras insisted I had to become the maintainer, before I could add anything.

I added 3 Fortran exercises in the last few days, but I'm thinking about what could be done across the Fortran/R/Julia tracks. Early days, but these are some preliminary ideas:

Slug	Julia	R	Fortran
rectangles	missing	missing	missing
line-up	missing	missing	missing
spiral-matrix	✅	missing	missing
state-of-tic-tac-toe	✅	missing	missing
two-bucket	✅	missing	missing
all-your-base	✅	✅	missing
flower-field	✅	✅	missing
game-of-life	✅	✅	missing
prime-factors	✅	✅	missing
pythagorean-triplet	✅	✅	missing

I'll aim to add the missing ones gradually, across the 3 tracks, until I get bored with iit

[depial]

Just one thing that could potentially use fixing. Otherwise everything looks good!

This is a well timed PR. I'm back from traveling, and trying to get back to productive ways after dragging my feet a bit. We'll see how quickly I can get back on track 😅