119 lines
2.5 KiB
Elixir
119 lines
2.5 KiB
Elixir
defmodule PatternMatching do
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use Koans
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koan "One matches one" do
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assert match?(1, ___)
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end
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koan "A value can be bound to a variable" do
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a = 1
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assert a == ___
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end
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koan "A variable can be rebound" do
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a = 1
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a = 2
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assert a == ___
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end
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koan "A variable can be pinned to be prevent it from being rebound" do
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a = 1
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assert_raise MatchError, fn() ->
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^a = ___
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end
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end
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koan "Patterns can be used to pull things apart" do
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[head | tail] = [1, 2, 3, 4]
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assert head == ___
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assert tail == ___
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end
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koan "And then put them back together" do
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head = 1
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tail = [2, 3, 4]
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assert ___ == [head | tail]
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end
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koan "Some values can be ignored" do
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[_first, _second, third, _fourth] = [1, 2, 3, 4]
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assert third == ___
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end
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koan "Strings come apart just as easily" do
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"Shopping list: " <> items = "Shopping list: eggs, milk"
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assert items == ___
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end
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koan "Maps support partial pattern matching" do
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%{make: make} = %{type: "car", year: 2016, make: "Honda", color: "black"}
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assert make == ___
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end
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koan "Lists must match exactly" do
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assert_raise ___, fn ->
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[a, b] = [1,2,3]
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end
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end
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koan "The pattern can make assertions about what it expects" do
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assert match?([1, _second, _third], ___)
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end
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def make_noise(%{type: "cat"}), do: "Meow"
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def make_noise(%{type: "dog"}), do: "Woof"
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def make_noise(_anything), do: "Eh?"
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koan "Functions perform pattern matching on their arguments" do
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cat = %{type: "cat"}
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dog = %{type: "dog"}
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snake = %{type: "snake"}
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assert make_noise(cat) == ___
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assert make_noise(dog) == ___
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assert make_noise(snake) == ___
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end
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koan "And they will only run the code that matches the argument" do
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name = fn
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("duck") -> "Donald"
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("mouse") -> "Mickey"
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(_other) -> "I need a name!"
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end
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assert name.("mouse") == ___
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assert name.("duck") == ___
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assert name.("donkey") == ___
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end
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koan "Errors are shaped differently than successful results" do
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dog = %{type: "dog"}
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result = case Map.fetch(dog, :type) do
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{:ok, value} -> value
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:error -> "not present"
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end
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assert result == ___
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end
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defmodule Animal do
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defstruct [:kind, :name]
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end
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koan "You can pattern match into the fields of a struct" do
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%Animal{name: name} = %Animal{kind: "dog", name: "Max"}
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assert name == ___
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end
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koan "Structs will even match with a regular map" do
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%{name: name} = %Animal{kind: "dog", name: "Max"}
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assert name == ___
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end
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end
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