Functional Programming in C#, Second Edition

11 Representing state and change

This chapter covers

• The pitfalls of state mutation
• Representing change without mutation
• Enforcing immutability
• Separating data and logic

Greek philosopher Heraclitus said that we cannot step into the same river twice; the river constantly changes, so the river that was there a moment ago is no longer. Many programmers would disagree, objecting that it’s the same river but its state has changed. Functional programmers try to stay true to Heraclitus’s thinking and would create a new river with every observation.

Most programs are built to represent things and processes in the real world, and because the world constantly changes, programs must somehow represent that change. The question is how we represent change. ...