Allows us to write Diagram B instead of Diagram B V2 Double/Float/Whatever in diagrams programs

[jeffreyrosenbluth]

Currently the linear changes has made the B token less useful since the type Diagram B V2 n the n depends on B the backend.
This provides the ability to switch backends simply by changing the import by using Diagram B instead of Diagram B V2 Double e.g.

• Companion branch in core

[jeffreyrosenbluth]

I can add this to the other backends if everyone likes it.
I'm also open to the names other than Figure.

[cchalmers]

I like the idea. How about abusing the existing V and N type families instead of making a new one?

type instance V SVG = V2
type instance N SVG = Double

type Figure b = Diagram b (V b) (N b)

-- possible (bad) examples
defaultRender :: Mainable (Figure b) => FilePath -> SizeSpec (V n) (N b) -> Figure b -> IO ()
forBackend :: SameSpace a b -> b -> a -> a

I'd also like to nominate the names Picture and Dia.

[jeffreyrosenbluth]

Yes that makes sense. I'll make the change and see check that it works.
I think we should probably go with Dia as a name as Picture is likely to conflict
with lots of other libraries.

[jeffreyrosenbluth]

@cchalmers Unfortunately, this does not seem to work.
The type checker can't seem to work it out and in diagrams
programs gives errors like "Expected type Dia B, Actual type Dia B"
pretty funny error though

[jeffreyrosenbluth]

I'm starting to like the pun Monogram fro monomorphic diagram instead
of Dia or Figure. Thoughts?

[cchalmers]

That's weird, it works when I try it.

I'm not sure about Monogram I like the pun but I don't really think about a diagram when I see it.

[jeffreyrosenbluth]

What do you mean works? It compiles fine but when I try it in a diagrams programs with serveral
Dia B type annotations it gets confused.

[jeffreyrosenbluth]

Here is a simple example

{-# LANGUAGE NoMonomorphismRestriction #-}

module Main where

import Diagrams.Prelude
import Diagrams.Backend.SVG.CmdLine

main = mainWith $ example # frame 1

c :: Dia B
c = circle 1 

s :: Dia B
s = square 2

example :: Dia B
example = c <> s

with error:
[1 of 1] Compiling Main ( Dia.hs, Dia.o )

Dia.hs:17:11:
Couldn't match type ‘V B’ with ‘V2’
Expected type: Dia B
Actual type: Dia B
In the first argument of ‘(<>)’, namely ‘c’
In the expression: c <> s

[cchalmers]

That example works. Couldn't match type ‘V B’ with ‘V2’ makes me think you didn't write

type instance V SVG = V2

If you did then that's very strange.

[jeffreyrosenbluth]

Yup I forgot that and type instance N SVG = Double
I'm still not loving Dia how about Illustration.

[fryguybob]

I'm not a fan of taking up more of the name space for a convenience. While it isn't the greatest I think it is less confusing to be something with Diagram in the name. Perhaps BDiagram for backend fixed diagram? Also do we gain anything by having the B argument? I seem to remember there were reasons for not going with type B = Diagram SVG R2 back when we introduced B, but I can't think of them now.

[jeffreyrosenbluth]

That's a good point about the name.
Maybe we should lose Diagram since it's barely better thatn QDiagram,
and swich Dia to Diagram.

I dont remember why we didn't use type B = ... either?

[byorgey]

Maybe we should lose Diagram since it's barely better thatn QDiagram,
and swich Dia to Diagram.

Yes, Diagram was originally intended to be essentially what you are discussing here (a convenient synonym that is sufficient for everyday use but hides some type complexity). So this sounds like a good route to me.

[jeffreyrosenbluth]

@byorgey nice to see you chiming in :)

[byorgey]

Well, you know, I'm all PhD'd and stuff now. =) I still have tons on my plate but I hope to be phasing back in a bit of time spent on diagrams.

[jeffreyrosenbluth]

Well I guess congratulations are in order Dr. Byorgey :D.
We all look forward to having you back.

[byorgey]

=D Thanks!

[jeffreyrosenbluth]

I think this, core and svg are ready to go.

[jeffreyrosenbluth]

I'd like to go ahead and merge all of these token branches. It's not a very controversial change and gets us back to why we created the Diagram type alias in the first place. Since the changes effect so many repos it will become a burden to sync them with main if some other branch is merged first.

As far as other aliases are concerned, as a library writer I'm happy to use the more verbose type e.g. QDiagram Cairo V2 Double Any. One can always define a convenient alias in a particular module or application program. In other words I don't think we should create too many aliases in -core.

[bergey]

I like the design currently in this branch, with Diagram B filling in the v and n for the Backend. +1 to merge.