EDIT (much later than original answer): MarkCC of Good Math, Bad Math recently wrote up an excellent discussion of the Halting problem with concrete examples. The halting problem is basically a formal way of asking if you can tell whether or not an arbitrary program will eventually halt. In other words, can you write a … Read more
The Internet itself pre-dates 1980, but the World Wide Web (“distributed hypertext via simple mechanisms”) as proposed and implemented by Tim Berners-Lee started in 1989/90. While the idea of hypertext had existed before (Nelson’s Xanadu had tried to implement a distributed scheme), the WWW was a new approach for implementing a distributed hypertext system. Berners-Lee … Read more
Given an arbitrary function, f, we define a function f’ which returns 1 on input n if f halts on input n. Now, for some number x we define a function g which, on input n, returns 1 if n = x, and otherwise calls f'(n). If functional equivalence were decidable, then deciding whether g … Read more
Code coverage is a measurement of how many lines/blocks/arcs of your code are executed while the automated tests are running. Code coverage is collected by using a specialized tool to instrument the binaries to add tracing calls and run a full set of automated tests against the instrumented product. A good tool will give you … Read more
I assume entropy was mentioned in the context of building decision trees. To illustrate, imagine the task of learning to classify first-names into male/female groups. That is given a list of names each labeled with either m or f, we want to learn a model that fits the data and can be used to predict … Read more
The term “referential transparency” comes from analytical philosophy, the branch of philosophy that analyzes natural language constructs, statements and arguments based on the methods of logic and mathematics. In other words, it is the closest subject outside computer science to what we call programming language semantics. The philosopher Willard Quine was responsible for initiating the … Read more
A Y-combinator is a “functional” (a function that operates on other functions) that enables recursion, when you can’t refer to the function from within itself. In computer-science theory, it generalizes recursion, abstracting its implementation, and thereby separating it from the actual work of the function in question. The benefit of not needing a compile-time name … Read more
Different. foreach iterates over a list and performs some operation with side effects to each list member (such as saving each one to the database for example) map iterates over a list, transforms each member of that list, and returns another list of the same size with the transformed members (such as converting a list … Read more
Type safety means that the compiler will validate types while compiling, and throw an error if you try to assign the wrong type to a variable. Some simple examples: // Fails, Trying to put an integer in a string String one = 1; // Also fails. int foo = “bar”; This also applies to method … Read more