Name Rascal/Declarations/AlgebraicDataType

Synopsis Define a user-defined type (Algebraic Data Type).

Syntax data Name = Alt1 | Alt2 | ... ;

Types Introduces the type Name and constructor functions for each alternative.

Description In ordinary programming languages record types or classes exist to introduce a new type name for a collection of related, named, values and to provide access to the elements of such a collection through their name.

In Rascal, algebraic data types provide this facility. They have to be declared, and then values can be declared using calls to the declared constructor functions, see Constructor.

Examples The following data declaration defines the datatype Bool that contains various constants (tt() and ff() and constructor functions conj and disj.

rascal>data Bool = tt() | ff() | conj(Bool L, Bool R)  | disj(Bool L, Bool R);
ok

terms of type Bool can be constructed using the defined constructors:

rascal>conj(tt(),ff());
Bool: conj(
  tt(),
  ff())

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