5.1: Abstract Data Types

Abstraction

Ignoring implementation details

Information Hiding

Hiding the complexity of programs

Purpose of abstraction

Provides an abstract view of a program; only needs to understand the abstract view to use it.

Modularity

Good approach to problem-solving to divide a problem into smaller independent problems

Functional Abstraction

Provided with:

• Inputs

• Outputs

• Pre-conditions

• Post-conditions

Don’t need to know how it works internally

Data Abstraction

Abstracts over data - does not specify how the data is implemented, nor how the functions manipulating the data are implemented

Abstract Data Type Components

• An abstract type name A

• An abstract interface to these operations

• A concrete representation type T

• Concrete implementation of operations on T

Haskell Modules

Used to define ADTs.

Module Components

• Data types

• Type declarations

• Functions

• Type signatures

• Type classes

• Instances of type classes

• Other kinds of declarations that we have not discussed yet

Type Classes

Provides a form of abstraction:

• A type class specifies an interface

• Specifies a class of types abstractly

• A member of that class must implement this interface

Object components

• Some internal state

• Methods to manipulate the state