I’ve finally sat down and played with Brent Yorgey’s diagrams package. Every once in a while, I just want to write something fun–some feel good code. Well, I had so much fun, I want to describe what I made.
It’s nothing complex or strange, it’s just a few shapes with some colors! (But the colors are so shiny and happy!)
Lets start from the top:
numCols, numRows :: Int numCols = 23 numRows = 5
Here, we just defined how many shapes wide and how many shapes tall we want our resulting diagram to be. Lets define
main :: IO () main = renderAs SVG "out2.svg" (Width width) dgram where width = (fromIntegral numCols) * 30
Alright, we know what
numCols is, and we see
width defined in the where clause, but what is
dgram :: Diagram dgram = vcat $ take numRows rows where rows = map hcat $ plines crps
dgram is the top level diagram we’re rendering.
vcat is a vertical concatenation of several other diagrams. We
take a specific number of rows from
rows–the horizontal concatenation (
hcat) of whatever is generated by
plines crps–and concatenate them together vertically.
Alright, we seem to be almost there now. What is
plines :: [Diagram] -> [[Diagram]] plines  =  plines pls = let (l,ls) = splitAt numCols pls in l : (plines ls)
As it turns out,
plines is just a cheap chunking function with a fixed chunk size. All this does is turn a list into a list of lists with the same length. If the sublists were concatenated back together again, you’d have your original list.
We’ve seen everything
plines has to offer, what about
crps :: [Diagram] crps = zipWith fillColor cs rps where rps = zipWith rotate rs ps rs = cycle . map (/ 4) $ [1..4] -- 4 rotations ps = cycle . map (flip regPoly 1) $ [3..7] -- 5 polygons cs = cycle [red,black,green,blue,yellow,violet] -- 6 colors
Hey! This is more interesting! Lets look a little closer at what’s happening here.
ps symbol defines an infinite list of cycling polygons. We use the regular polygon (
regPoly) function to generate polygons with 3, 4, 5, 6, and 7 sides. The
cs symbol is just defining an infinite list of colors–nothing too complex here. The
rs symbol is a cycling list of 1/4, 2/4, 3/4, and 4/4. These are used as rotations in terms of turns.
Now, what is that
rps symbol? Lets see, we are zipping
ps together using the function
rotate which accepts a Double representing a fraction of a turn and a Diagram to rotate. So,
rps is an infinite list of cycling polygons where each successive polygon is rotated one quarter turn more than the previous.
This means that
crps is an infinite list of cycling polygons each rotated one quarter turn more than the previous polygon but and each polygon has a cycling fill color! Neat!
So what does this look like?
I don’t know about you, but that takes me back to grade school. Sometimes a little bit of happy code can brighten your day!