Pierre-Yves Saumont [Pierre-Yves Saumont] - Functional Programming in Java: How functional techniques improve your Java programs

Functional programs contain no assignment statements, so variables, once given a value, never change. More generally, functional programs contain no side-effects at all. A function call can have no effect other than to compute its result. This eliminates a major source of bugs, and also makes the order of execution irrelevantsince no side-effect can change an expressions value, it can be evaluated at any time. This relieves the programmer of the burden of prescribing the flow of control. Since expressions can be evaluated at any time, one can freely replace variables by their values and vice versathat is, programs are referentially transparent. This freedom helps make functional programs more tractable mathematically than their conventional counterparts.

John Hughes Why Functional Programming Matters

I call it my billion-dollar mistake ... My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But I couldnt resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.

Tony Hoare

Program testing can be a very effective way to show the presence of bugs, but is hopelessly inadequate for showing their absence.

Edsger W. Dijkstra

Testing by itself does not improve software quality. Test results are an indicator of quality, but in and of themselves, they dont improve it. Trying to improve software quality by increasing the amount of testing is like trying to lose weight by weighing yourself more often.

Steve McConnell

The proper use of comments is to compensate for our failure to express ourselves in code.

Robert C. Martin

In programming the hard part isnt solving problems, but deciding what problems to solve.

Paul Graham

Object oriented programming makes code understandable by encapsulating moving parts. Functional programming makes code understandable by minimizing moving parts.

Michael Feathers

I have always found that plans are useless, but planning is indispensable.

Dwight D. Eisenhower

There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies and the other way is to make it so complicated that there are no obvious deficiencies. The first method is far more difficult.

Tony Hoare

If wed asked the customers what they wanted, they would have said faster horses.

Henry Ford

Whereas some declarative programmers only pay lip service to equational reasoning, users of functional languages exploit them every time they run a compiler, whether they notice it or not.

Philip Wadler How to declare an imperative

We were not out to win over the Lisp programmers; we were after the C++ programmers. We managed to drag a lot of them about halfway to Lisp.

Guy Steele

People get types. They use them all the time. Telling someone he cant pound a nail with a banana doesnt much surprise him.

Unknown

TDD replaces a type checker ... in the same way that a strong drink replaces sorrows.

byorgey

Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it.

Brian W. Kernighan and P. J. Plauger

As soon as we started programming, we found to our surprise that it wasnt as easy to get programs right as we had thought. Debugging had to be discovered. I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs.

Maurice Wilkes (1949)