Synopsis Constructors create values for user-defined datatypes (Algebraic Datatypes).
Syntax
Name ( Exp1, Exp2, ... )
Types
Exp1 | Exp2 | ... | Name ( Exp1, Exp2, ... ) |
|---|---|---|---|
T1 | T2 | ... | depends on ADT declaration |
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, see AlgebraicDataType, and then values can be created using calls to the declared constructor functions. The constructor
First, the actual parameter expressions
Observe that the syntax of a constructor is identical to the syntax of an function Call.
In Rascal, algebraic data types provide this facility. They have to be declared, see AlgebraicDataType, and then values can be created using calls to the declared constructor functions. The constructor
Name should correspond (regarding name, arity and argument types) to one of the alternatives
in the ADT declaration.
First, the actual parameter expressions
Expi are evaluated resulting in values Vi.
Next, a data value is constructed in accordance with the declared data type
using the values Vi as arguments for the constructor. This data value is used as value of the constructor.
Constructors are functions that can be used in all contexts where functions can be used.
Observe that the syntax of a constructor is identical to the syntax of an function Call.
Examples First, define a datatype
WF for word frequencies:
rascal>data WF = wf(str word, int freq);
ok
Then construct a new WF value by calling the constructor wf with appropriate arguments:
rascal>wf("Rascal", 10000);
WF: wf("Rascal",10000)