Programming Visual Basic 2008

Chapter 9. Functional Programming

In this chapter, we’ll cover two major Visual Basic programming topics: lambda expressions and error handling. Both are mysterious, one because it uses a Greek letter in its name and the other because it might as well be in Greek for all the difficulty programmers have with it. Lambda expressions in particular have to do with the broader concept of functional programming, the idea that every computing task can be expressed as a function and that functions can be passed around willy-nilly within the source code. Visual Basic is not a true functional programming language, but the introduction of lambda expressions in Visual Basic 2008 brings some of those functional ways and means to the language.

Lambda Expressions

Lambda expressions are named for lambda calculus (or λ-calculus), a mathematical system designed in the 1930s by Alonzo Church, certainly a household name between the wars. Although his work was highly theoretical, it led to features and structures that benefit most programming languages today. Specifically, lambda calculus provides the rationale for the Visual Basic functions, arguments, and return values that we’ve already learned about. So, why add a new feature to Visual Basic and call it “lambda” when there are lambda things already in the language? Great question. No answer.

Lambda expressions let you define an object that contains an entire function. Although this is something new in Visual Basic, a similar feature has existed ...