An AND is true only if both of the operands evaluate to true. Most languages have what’s called short circuiting behavior for a logical AND ( &). When it encounters an already evaluated variable, it can simply look up the value in the dictionary.Īside from performance benefits, there are a couple of other things that make lazy evaluation really cool. In other words, it needs to keep a dictionary where the key is the name of the variable, and the value is the result of the evaluation. For lazy evaluation to be efficient, it needs to use memoization. Just like lazy students, a lazy compiler can be much more efficient if it makes smart choices. All right, I’ll evaluate your darn expression.” Instead, it will postpone the evaluation until it’s absolutely needed, and only then will it say, “Sigh.

It will not be a good student and study in advance. It’s called “lazy” because the compiler will procrastinate. The style of only evaluating what's needed is called lazy evaluation, while the opposite (evaluating immediately) is called strict evaluation. In the example above there is no point in evaluating 3 + 2, because it's not used. def someFunction(x, y) = return x + 1 someFunction(3, 3 + 2) For instance, function parameters might go unused, so we don’t need to evaluate them. Not all expressions are worth evaluating. While most languages do this immediately, it’s not very efficient. If 'she' was defined earlier, it will evaluate to a pointer to a person. Our brains also do this: when somebody tells you, 'She's a good programmer!', your brain is evaluating the 'she' in the sentence.

Evaluation is the process of getting the root meaning of a piece of code. When a compiler encounters an expression, usually it tries to evaluate it. What is Lazy Evaluation? - Programming Word of the Day

What is the opposite of lazy