Every so often I see a question on SO which forces me to spend half an hour editing a really bad Wikipedia article. The article is now only moderately bad. In the part that bears on your question, I wrote as follows: In computer science, a function or expression is said to have a side … Read more
The entire reason lambda exists is that it’s an expression.1 If you want something that’s like lambda but is a statement, that’s just def. Python expressions cannot contain statements. This is, in fact, fundamental to the language, and Python gets a lot of mileage out of that decision. It’s the reason indentation for flow control … Read more
Side effects are the easier concept. A “pure function” is a function that maps its input value(s) into an output value function plus(x, y) { return x + y; }. A “side effect” is any effect other than that return value. So, for instance: function plusWithSideEffects(x, y) { alert(‘This is a side effect’); return x … Read more
What alternatives are there to monads for I/O in a pure functional language? I’m aware of two alternatives in the literature: One is a so-called linear type system. The idea is that a value of linear type must be used exactly one time: you can’t ignore it, and you can’t use it twice. With this … Read more
The behaviour of a C program that executes the expression i == (i = 2) is undefined. It comes from C11 6.5p22: If a side effect on a scalar object is unsequenced relative to either a different side effect on the same scalar object or a value computation using the value of the same scalar … Read more
A side effect is an observable interaction with its environment (apart from computing its result value). In Haskell, we try hard to avoid functions with such side effects. This even applies to IO actions: when an IO action is evaluated, no side effects are performed, they are executed only when the actions prescribed in the … Read more
The other answers are looking at it from a technical point of view (i.e. what’s the best way to modify a list), but I would say the (much) more important reason people recommend, for example, slicing, is that it doesn’t modify the original list. The reason for this in turn is that usually, the list … Read more
Purity is only violated if you observe the exception, and make a decision based on it that changes the control flow. Actually throwing an exception value is referentially transparent — it is semantically equivalent to non-termination or other so-called bottom values. If a (pure) function is not total, then it evaluates to a bottom value. … Read more
If I gather in one place any three theorists of my acquaintance, at least two of them disagree on the meaning of the term “referential transparency.” And when I was a young student, a mentor of mine gave me a paper explaining that even if you consider only the professional literature, the phrase “referentially transparent” … Read more
Sean from the webpack Team! I’ll do my best in lieu of our documentation still in progress to answer your question here! According to the ECMA Module Spec (I’m not going to try and find the link so you’ll have to trust me here because it’s buried), whenever a module re-exports all exports, (regardless if … Read more