haskell-type-classes.ipynb

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    "{-\n",
    "interface Equality<T> {\n",
    "  boolean isEqual(T x, T y);\n",
    "}\n",
    "-}\n",
    "\n",
    "class Equality a where\n",
    "  isEqual :: a -> a -> Bool"
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    "data Point = Point Int Int\n",
    "\n",
    "instance Equality Point where\n",
    "  isEqual (Point ax ay) (Point bx by) = ax == bx && ay == by"
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       "type Point :: *\n",
       "data Point = Point Int Int\n",
       "  \t-- Defined at <interactive>:1:1\n",
       "instance [safe] Equality Point -- Defined at <interactive>:2:10"
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    ":i Point"
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    "contains :: Equality a => [a] -> a -> Bool\n",
    "contains [] _ = False\n",
    "contains (x:xs) target = if isEqual x target then True else contains xs target"
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    "contains [Point 1 1, Point 1 2] (Point 1 4)"
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    "id :: a -> a\n",
    "pair :: a -> (a, a)\n",
    "singleton :: a -> [a]"
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   "source": [
    "instance Equality a => Equality (Maybe a) where\n",
    "  isEqual Nothing Nothing = True\n",
    "  isEqual (Just x) (Just y) = isEqual x y\n",
    "  isEqual _ _ = False"
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    "contains [Nothing, Just (Just (Point 1 1))] (Just (Just (Point 1 2)))"
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