terminology

Could someone provide a good description of what a Lambda is? We have a tag for them and they're on the secrets of C# question, but I have yet to find a good definition and explanation of what they are in the first place. Closures, lambdas, and anonymous functions are not necessarily the same thing. An anonymous function is any function that doesn't have (or, at least, need) its own name. A closure is a function that can access variables that were in its lexical scope when it was declared, even after they have fallen out of scope. Anonymous functions do not necessarily have to be closures, but

What does the word "literal" mean when used in context such as literal strings and literal values? What is the difference between a literal value and a value? A literal is "any notation for representing a value within source code" ( wikipedia ) (Contrast this with identifiers , which refer to a value in memory.) Examples: "hey" (a string) false (a boolean) 3.14 (a real number) [1,2,3] (a list of numbers) (x) => x*x (a function) /^1?$|^(11+?)\1+$/ (a regexp) Some things that are not literals: std::cout (an identifier) foo = 0; (a statement) 1+2 (an expression) A literal is a value that has been

Consider a single-linked list. It looks something like data List x = Node x (List x) | End It is natural to define a folding function such as reduce :: (x -> y -> y) -> y -> List x -> y In a sense, reduce f x0 replaces every Node with f and every End with x0 . This is what the Prelude refers to as a fold . Now consider a simple binary tree: data Tree x = Leaf x | Branch (Tree x) (Tree x) It is similarly natural to define a function such as reduce :: (y -> y -> y) -> (x -> y) -> Tree x -> y Notice that this reduction has a quite different character; whereas the list-based one is inherently