To answer your first question, mathematical functions have often been described as “pure” in terms of some specified variables. e.g.: the first term is a pure function of x and the second term is a pure function of y Because of this, I don’t think you’ll find a true “first” occurrence. For programming languages, a … Read more
An idempotent function can cause idempotent side-effects. A pure function cannot. For example, a function which sets the text of a textbox is idempotent (because multiple calls will display the same text), but not pure. Similarly, deleting a record by GUID (not by count) is idempotent, because the row stays deleted after subsequent calls. (additional … Read more
Here are a few counterexamples that do not change the outer scope but are still considered impure: function a() { return Date.now(); } function b() { return window.globalMutableVar; } function c() { return document.getElementById(“myInput”).value; } function d() { return Math.random(); } (which admittedly does change the PRNG, but is not considered observable) Accessing non-constant non-local … Read more
No, it’s not. Given the same input, this function will return different values. And then you can’t build a ‘table’ that maps the input and the outputs. From the Wikipedia article for Pure function: The function always evaluates the same result value given the same argument value(s). The function result value cannot depend on any … Read more