Color Operator Precedence

Temurson commented 4 years ago

I found probably unexpected behavior of operators +., -., *. in Color.hs module. Example with steps to reproduce (starting at the project root):

$ ghci
GHCi, version 8.8.1: https://www.haskell.org/ghc/  :? for help\n
Prelude> :set -isrc
Prelude> :l src/Clay/Color
[1 of 3] Compiling Clay.Property    ( src/Clay/Property.hs, interpreted )
[2 of 3] Compiling Clay.Common      ( src/Clay/Common.hs, interpreted )
[3 of 3] Compiling Clay.Color       ( src/Clay/Color.hs, interpreted )
Ok, three modules loaded.
*Clay.Color> c = white
*Clay.Color> c
Rgba 255 255 255 1.0
*Clay.Color> c -. 25 +. 5 * 5
<interactive>:7:1: error:
    • No instance for (Num Color) arising from a use of ‘*’
    • In the expression: c -. 25 +. 5 * 5
      In an equation for ‘it’: it = c -. 25 +. 5 * 5
*Clay.Color> :info +.
(+.) :: Color -> Integer -> Color
        -- Defined at src/Clay/Color.hs:123:1
*Clay.Color> c -. 25 +. (5 * 5)
Rgba 255 255 255 1.0

Note that when doing :info +. in ghci, it does not show precedence, and if you check the definition, there is no precedence there too. I suspect the problem here is that +., -. and *. (the only three defined in Color.hs) have precedence higher than *, which doesn't really make sense. I do not know what is default operator precedence in Haskell, and I always thought that it is required to specify precedence when declaring custom operators, but I could not find it within the entire Clay code. I think this should be fixed by explicitly specifying operator precedence of +., -. and *. in Color.hs.

Temurson commented 4 years ago

I have tried adding infixl 6 +., infixl 6 -. and infixl 7 *. to Color.hs, and this resolved this strange behavior. Note that these precedence values match those of regular operators. Let me know if this is something that should be resolved, and I will create a PR.