Heatmap Example just isn't building

[MilesLitteral]

I made a test to use the heatmap example in:

import Plots
import Linear.V2 
import Control.Lens

main :: IO ()
main = do
    let xs = [[1,2,3],[4,5,6]]
    heatMap xs $ heatMapSize .= V2 10 10

But it fails and is unbuildable with the following errors:

    • No instance for (base-4.15.1.0:Data.Typeable.Internal.Typeable
                         a0)
        arising from a use of ‘heatMap’
    • In the first argument of ‘($)’, namely ‘heatMap xs’
      In a stmt of a 'do' block: heatMap xs $ (heatMapSize .= V2 10 10)
      In the expression:
        do let xs = ...
           heatMap xs $ (heatMapSize .= V2 10 10)
   |
19 |     heatMap xs $ (heatMapSize .= V2 10 10)


    • Ambiguous type variable ‘a0’ arising from the literal ‘10’
      prevents the constraint ‘(Num a0)’ from being solved.
      Probable fix: use a type annotation to specify what ‘a0’ should be.
      These potential instances exist:
        instance Num a => Num (Identity a)
          -- Defined in ‘Data.Functor.Identity’
        instance Num a => Num (V2 a) -- Defined in ‘Linear.V2’
        instance Num Integer -- Defined in ‘GHC.Num’
        ...plus four others
        ...plus 10 instances involving out-of-scope types
        (use -fprint-potential-instances to see them all)
    • In the first argument of ‘V2’, namely ‘10’
      In the second argument of ‘(.=)’, namely ‘V2 10 10’
      In the second argument of ‘($)’, namely ‘(heatMapSize .= V2 10 10)’
   |
19 |     heatMap xs $ (heatMapSize .= V2 10 10)
   |                                     ^^

I took out heatMapAxis because it keeps complaining that it's constraint (Axis B V2 Double)
is unsolvable in terms of B and I don't understand how to remedy it not finding a backend.
There doesn't seem to be a lens for it, or any reference to the backend being used but
considering it's capitalized there has to be something?

Any advice is appreciated, Thanks

[MilesLitteral]

I wanted to add on that writing the heatmap example like this also doesn't work

import Plots
import Linear.V2 
import Control.Lens

heatMapAxis :: Axis B V2 Double
heatMapAxis = r2Axis &~ do
  display colourBar
  axisExtend .= noExtend

  let xs = [[1,2,3],[4,5,6]]
  heatMap xs $ heatMapSize .= V2 10 10

instead it throws this error

    Not in scope: type constructor or class ‘B’
  |
5 | heatMapAxis :: Axis B V2 Double
  |                     ^

[cchalmers]

You need to import a backend. Each backend exports a B type alias to make it easier to switch between backends. You can see some examples that hopefully still compile in https://github.com/cchalmers/plots/tree/master/examples. I don't have a heatMap example there but they should work the same. Those examples import Diagrams.Backend.Rasterific.CmdLine for the backend.

[MilesLitteral]

Thanks! This updated version of the example code builds

{-# LANGUAGE FlexibleContexts #-}
module Main where 

import Plots
import Linear.V2 
import Control.Lens
import Control.Monad.IO.Class
import Diagrams.Backend.Rasterific.CmdLine

heatMapAxis :: Axis B V2 Double
heatMapAxis = r2Axis &~ do
  display colourBar
  axisExtend .= noExtend

  let xs = [[1,2,3],[4,5,6]]
  heatMap xs $ heatMapSize .= V2 10 10

main :: IO ()
main =  r2AxisMain $ heatMapAxis

when running the example GHC points out as follows:
No output file given. Specify output file with -o

Is this the only way to force the output of the heatmap? Is there a way to SaveImage (like JuicyPixels)

Thank you very much your answered fixed the original problem and addressed my original question :)

[MilesLitteral]

as a poor man's work around I discovered you can do this:

{-# LANGUAGE FlexibleContexts #-}

module Main where 

import Plots
import Linear.V2 
import Control.Lens
import Control.Monad.IO.Class

import Codec.Picture
import Diagrams.Backend.Rasterific.CmdLine

heatMapIndexedAxis :: Axis B V2 Double
heatMapIndexedAxis = r2Axis &~ do
  display colourBar
  axisExtend .= noExtend

  let f (V2 x y) = fromIntegral x + fromIntegral y
  heatMapIndexed (V2 3 3) f $ heatMapSize .= V2 10 10
  
main :: IO ()
main =  r2AxisMain $ heatMapIndexedAxis

Then run this in cmd:
stack exec --<module> -o out.png

I'm sure a more standard solution will come up in time; thanks again for your help!

[cchalmers]

Happy to help. Yes, rendering directly is possible. You can call renderAxis and then run renderRasterific on the resulting Diagram.