Enumerated Type - Algebraic Data Type in Functional Programming

Algebraic Data Type in Functional Programming

In functional programming languages in the ML lineage (e.g., SML, OCaml and Haskell), an algebraic data type with only nullary constructors can be used to implement an enumerated type. For example (in the syntax of SML signatures):

datatype cardsuit = Clubs | Diamonds | Hearts | Spades type card = { suit: cardsuit; value: int } val hand : card list val trump : cardsuit

In these languages the small-integer representation is completely hidden from the programmer, if indeed such a representation is employed by the implementation. However, Haskell has the Enum type class which a type can derive or implement to get a mapping between the type and Int.

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