[Haskell-beginners] cabal.config (sandbox) with Chart package

[Jack Vice]

I am attempting my first sandbox build with a cabal package (Chart) and I
don't know what to put in my cabal.config file after looking at these sites:
https://www.haskell.org/cabal/users-guide/developing-packages.html
http://coldwa.st/e/blog/2013-08-20-Cabal-sandbox.html
https://wiki.haskell.org/Cabal-Install

I am getting the following build error:
*Building chartHask-0.1.0.0...*
*Preprocessing executable 'chartHask' for chartHask-0.1.0.0...*
*[1 of 1] Compiling Main             ( Main.hs,
dist/build/chartHask/chartHask-tmp/Main.o )*

*Main.hs:5:1: error:*
*    Failed to load interface for ‘Graphics.Rendering.Chart.Backend.Cairo’*
*    Perhaps you meant*
*      Graphics.Rendering.Chart.Backend.Impl (from Chart-1.9)*
*      Graphics.Rendering.Chart.Backend.Types (from Chart-1.9)*
*      Graphics.Rendering.Chart.Backend (from Chart-1.9)*
*    Use -v to see a list of the files searched for.*

So, Maybe I'm dumb or it's not explicit (or both) on how to add a package
to my cabal.config so it can find it and build.  I tried adding this to my
cabal.config to no avail:
*documentation: True*
*constraints: Chart >= 1.9*

Main.hs (from Chart example:
*module Main where*

*import Graphics.Rendering.Chart.Easy*
*import Graphics.Rendering.Chart.Backend.Cairo*

*signal :: [Double] -> [(Double,Double)]*
*signal xs = [ (x,(sin (x*3.14159/45) + 1) / 2 * (sin (x*3.14159/5))) | x
<- xs ]*

*main = toFile def "example1_big.png" $ do*
*    layout_title .= "Amplitude Modulation"*
*    setColors [opaque blue, opaque red]*
*    plot (line "am" [signal [0,(0.5)..400]])*
*    plot (points "am points" (signal [0,7..400]))*

Or should I be using Stack? (probably private email or new thread question)
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