Concrete data type
A concrete data type is an opposite of an Abstract data type. It is a specialized solution-oriented data type that represents a well-defined single solution domain concept. A concrete data type is rarely reusable beyond its original use, but can be embedded or composed with other data types to form larger data types.
For example, a data type representing "parse tree for Haskell" is likely to be a concrete data type, whereas a "tree" data type is a corresponding Abstract data type.
In Haskell, concrete data types can be introduced withthe data construct (without parameters), or by specializing a Parametrized data type to a specific situation. For example,