Real World Haskell - 第3章 Part3 Algebraic data types

Haskell プログラミング

Real World Haskell で Haskell を継続的に勉強中。

Defining Types, Streamlining Functions

Chapter 3. Defining Types, Streamlining Functions

Algebraic data types
  • algebraic data type は value constructor を複数持てる
data Bool = False | True

type CardHolder = String
type CardNumber = String
type Address = [String]

data BillingInfo = CreditCard CardNumber CardHolder Address
                 | CashOnDelivery
                 | Invoice CustomerID
                   deriving (Show)
  • Algebraic data types は構造が同じだけど意味が違うデータを区別できる
    • tuple では無理

If you're using compound values widely in your code (as almost all non-trivial programs do), adding data declarations will benefit you in both type safety and readability.

  • C/C++ の struct との違い

The main difference between the two is that the fields in the Haskell type are anonymous and positional.

In C, the elements of an enum are integers.

  • C/C++ の union との違い

A big difference between the two is that a union doesn't tell us which alternative is actually present;

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