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| 1 | +defmodule WithStatement do |
| 2 | + @moduledoc false |
| 3 | + use Koans |
| 4 | + |
| 5 | + @intro "The With Statement - Elegant error handling and happy path programming" |
| 6 | + |
| 7 | + koan "With lets you chain operations that might fail" do |
| 8 | + parse_and_add = fn str1, str2 -> |
| 9 | + with {:ok, a} <- Integer.parse(str1), |
| 10 | + {:ok, b} <- Integer.parse(str2) do |
| 11 | + {:ok, a + b} |
| 12 | + else |
| 13 | + :error -> {:error, :invalid_number} |
| 14 | + end |
| 15 | + end |
| 16 | + |
| 17 | + assert parse_and_add.("5", "4") == ___ |
| 18 | + assert parse_and_add.("abc", "1") == ___ |
| 19 | + end |
| 20 | + |
| 21 | + koan "With short-circuits on the first non-matching pattern" do |
| 22 | + process_user = fn user_data -> |
| 23 | + with {:ok, name} <- Map.fetch(user_data, :name), |
| 24 | + {:ok, age} <- Map.fetch(user_data, :age), |
| 25 | + true <- age >= 18 do |
| 26 | + {:ok, "Adult user: #{name}"} |
| 27 | + else |
| 28 | + :error -> {:error, :missing_data} |
| 29 | + false -> {:error, :underage} |
| 30 | + end |
| 31 | + end |
| 32 | + |
| 33 | + assert process_user.(%{name: "Alice", age: 25}) == ___ |
| 34 | + assert process_user.(%{name: "Bob", age: 16}) == ___ |
| 35 | + assert process_user.(%{age: 25}) == ___ |
| 36 | + end |
| 37 | + |
| 38 | + defp safe_divide(_, 0), do: {:error, :division_by_zero} |
| 39 | + defp safe_divide(x, y), do: {:ok, x / y} |
| 40 | + |
| 41 | + defp safe_sqrt(x) when x < 0, do: {:error, :negative_sqrt} |
| 42 | + defp safe_sqrt(x), do: {:ok, :math.sqrt(x)} |
| 43 | + |
| 44 | + koan "With can handle multiple different error patterns" do |
| 45 | + divide_and_sqrt = fn x, y -> |
| 46 | + with {:ok, division} <- safe_divide(x, y), |
| 47 | + {:ok, sqrt} <- safe_sqrt(division) do |
| 48 | + {:ok, sqrt} |
| 49 | + else |
| 50 | + {:error, :division_by_zero} -> {:error, "Cannot divide by zero"} |
| 51 | + {:error, :negative_sqrt} -> {:error, "Cannot take square root of negative number"} |
| 52 | + end |
| 53 | + end |
| 54 | + |
| 55 | + assert divide_and_sqrt.(16, 4) == ___ |
| 56 | + assert divide_and_sqrt.(10, 0) == ___ |
| 57 | + assert divide_and_sqrt.(-16, 4) == ___ |
| 58 | + end |
| 59 | + |
| 60 | + koan "With works great for nested data extraction" do |
| 61 | + get_user_email = fn data -> |
| 62 | + with {:ok, user} <- Map.fetch(data, :user), |
| 63 | + {:ok, profile} <- Map.fetch(user, :profile), |
| 64 | + {:ok, email} <- Map.fetch(profile, :email), |
| 65 | + true <- String.contains?(email, "@") do |
| 66 | + {:ok, email} |
| 67 | + else |
| 68 | + :error -> {:error, :missing_data} |
| 69 | + false -> {:error, :invalid_email} |
| 70 | + end |
| 71 | + end |
| 72 | + |
| 73 | + valid_data = %{ |
| 74 | + user: %{ |
| 75 | + profile: %{ |
| 76 | + email: "user@example.com" |
| 77 | + } |
| 78 | + } |
| 79 | + } |
| 80 | + |
| 81 | + invalid_email_data = %{ |
| 82 | + user: %{ |
| 83 | + profile: %{ |
| 84 | + email: "notanemail" |
| 85 | + } |
| 86 | + } |
| 87 | + } |
| 88 | + |
| 89 | + assert get_user_email.(valid_data) == ___ |
| 90 | + assert get_user_email.(invalid_email_data) == ___ |
| 91 | + assert get_user_email.(%{}) == ___ |
| 92 | + end |
| 93 | + |
| 94 | + koan "With can combine pattern matching with guards" do |
| 95 | + process_number = fn input -> |
| 96 | + with {:ok, num} <- Integer.parse(input), |
| 97 | + true <- num > 0, |
| 98 | + result when result < 1000 <- num * 10 do |
| 99 | + {:ok, result} |
| 100 | + else |
| 101 | + :error -> {:error, :not_a_number} |
| 102 | + false -> {:error, :not_positive} |
| 103 | + result when result >= 1000 -> {:error, :result_too_large} |
| 104 | + end |
| 105 | + end |
| 106 | + |
| 107 | + assert process_number.("5") == ___ |
| 108 | + assert process_number.("-5") == ___ |
| 109 | + assert process_number.("150") == ___ |
| 110 | + assert process_number.("abc") == ___ |
| 111 | + end |
| 112 | + |
| 113 | + koan "With clauses can have side effects and assignments" do |
| 114 | + register_user = fn user_data -> |
| 115 | + with {:ok, email} <- validate_email(user_data[:email]), |
| 116 | + {:ok, password} <- validate_password(user_data[:password]), |
| 117 | + hashed_password = hash_password(password), |
| 118 | + {:ok, user} <- save_user(email, hashed_password) do |
| 119 | + {:ok, user} |
| 120 | + else |
| 121 | + {:error, reason} -> {:error, reason} |
| 122 | + end |
| 123 | + end |
| 124 | + |
| 125 | + user_data = %{email: "test@example.com", password: "secure123"} |
| 126 | + assert register_user.(user_data) == ___ |
| 127 | + end |
| 128 | + |
| 129 | + defp validate_email(email) when is_binary(email) and byte_size(email) > 0 do |
| 130 | + if String.contains?(email, "@"), do: {:ok, email}, else: {:error, :invalid_email} |
| 131 | + end |
| 132 | + |
| 133 | + defp validate_email(_), do: {:error, :invalid_email} |
| 134 | + |
| 135 | + defp validate_password(password) when is_binary(password) and byte_size(password) >= 6 do |
| 136 | + {:ok, password} |
| 137 | + end |
| 138 | + |
| 139 | + defp validate_password(_), do: {:error, :weak_password} |
| 140 | + |
| 141 | + defp hash_password(password), do: "hashed_" <> password |
| 142 | + |
| 143 | + defp save_user(email, hashed_password) do |
| 144 | + {:ok, %{id: 1, email: email, password: hashed_password}} |
| 145 | + end |
| 146 | + |
| 147 | + koan "With can be used without an else clause for simpler cases" do |
| 148 | + simple_calculation = fn x, y -> |
| 149 | + with num1 when is_number(num1) <- x, |
| 150 | + num2 when is_number(num2) <- y do |
| 151 | + num1 + num2 |
| 152 | + end |
| 153 | + end |
| 154 | + |
| 155 | + assert simple_calculation.(5, 3) == ___ |
| 156 | + # When pattern doesn't match and no else, returns the non-matching value |
| 157 | + assert simple_calculation.("5", 3) == ___ |
| 158 | + end |
| 159 | + |
| 160 | + # TODO: Is there any reason the mix the case and with here? Can't they be |
| 161 | + # combined? I'm not sure what the point is. |
| 162 | + koan "With integrates beautifully with pipe operators" do |
| 163 | + process_order = fn order_data -> |
| 164 | + order_data |
| 165 | + |> validate_order() |
| 166 | + |> case do |
| 167 | + {:ok, order} -> |
| 168 | + with {:ok, payment} <- process_payment(order), |
| 169 | + {:ok, shipment} <- create_shipment(order, payment) do |
| 170 | + {:ok, %{order: order, payment: payment, shipment: shipment}} |
| 171 | + end |
| 172 | + |
| 173 | + error -> |
| 174 | + error |
| 175 | + end |
| 176 | + end |
| 177 | + |
| 178 | + valid_order = %{item: "book", price: 20, customer: "alice"} |
| 179 | + assert process_order.(valid_order) == ___ |
| 180 | + end |
| 181 | + |
| 182 | + defp validate_order(%{item: item, price: price, customer: customer}) |
| 183 | + when is_binary(item) and is_number(price) and price > 0 and is_binary(customer) do |
| 184 | + {:ok, %{item: item, price: price, customer: customer, id: 123}} |
| 185 | + end |
| 186 | + |
| 187 | + defp validate_order(_), do: {:error, :invalid_order} |
| 188 | + |
| 189 | + defp process_payment(%{price: price}) when price > 0 do |
| 190 | + {:ok, %{amount: price, status: "paid", id: 456}} |
| 191 | + end |
| 192 | + |
| 193 | + defp create_shipment(%{customer: customer}, %{status: "paid"}) do |
| 194 | + {:ok, %{customer: customer, status: "shipped", tracking: "ABC123"}} |
| 195 | + end |
| 196 | + |
| 197 | + koan "With can handle complex nested error scenarios" do |
| 198 | + complex_workflow = fn data -> |
| 199 | + with {:ok, step1} <- step_one(data), |
| 200 | + {:ok, step2} <- step_two(step1), |
| 201 | + {:ok, step3} <- step_three(step2) do |
| 202 | + {:ok, step3} |
| 203 | + else |
| 204 | + {:error, :step1_failed} -> {:error, "Failed at step 1: invalid input"} |
| 205 | + {:error, :step2_failed} -> {:error, "Failed at step 2: processing error"} |
| 206 | + {:error, :step3_failed} -> {:error, "Failed at step 3: final validation error"} |
| 207 | + other -> {:error, "Unexpected error: #{inspect(other)}"} |
| 208 | + end |
| 209 | + end |
| 210 | + |
| 211 | + assert complex_workflow.("valid") == ___ |
| 212 | + assert complex_workflow.("step1_fail") == ___ |
| 213 | + assert complex_workflow.("step2_fail") == ___ |
| 214 | + end |
| 215 | + |
| 216 | + defp step_one("step1_fail"), do: {:error, :step1_failed} |
| 217 | + defp step_one(data), do: {:ok, "step1_" <> data} |
| 218 | + |
| 219 | + defp step_two("step1_step2_fail"), do: {:error, :step2_failed} |
| 220 | + defp step_two(data), do: {:ok, "step2_" <> data} |
| 221 | + |
| 222 | + defp step_three("step2_step1_step3_fail"), do: {:error, :step3_failed} |
| 223 | + defp step_three(data), do: {:ok, "step3_" <> data} |
| 224 | +end |
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