Merge pull request #93 from purescript/doc-updates

Fix typo, document non-law-abiding numeric instances

Author: garyb

src/Data/Eq.purs

@@ -10,6 +10,11 @@ import Data.Void (Void)
 -- | - Reflexivity: `x == x = true`
 -- | - Symmetry: `x == y = y == x`
 -- | - Transitivity: if `x == y` and `y == z` then `x == z`
+-- |
+-- | **Note:** The `Number` type is not an entirely law abiding member of this
+-- | class due to the presence of `NaN`, since `NaN /= NaN`. Additionally,
+-- | computing with `Number` can result in a loss of precision, so sometimes
+-- | values that should be equivalent are not.
 class Eq a where
   eq :: a -> a -> Boolean
 

src/Data/Semiring.purs

@@ -17,7 +17,12 @@ import Data.Unit (Unit, unit)
 -- | - Multiplication distributes over addition:
 -- |   - Left distributivity: `a * (b + c) = (a * b) + (a * c)`
 -- |   - Right distributivity: `(a + b) * c = (a * c) + (b * c)`
--- | - Annihiliation: `zero * a = a * zero = zero`
+-- | - Annihilation: `zero * a = a * zero = zero`
+-- |
+-- | **Note:** The `Number` and `Int` types are not fully law abiding
+-- | members of this class hierarchy due to the potential for arithmetic
+-- | overflows, and in the case of `Number`, the presence of `NaN` and
+-- | `Infinity` values. The behaviour is unspecified in these cases.
 class Semiring a where
   add  :: a -> a -> a
   zero :: a