Found in the Darnedest Places
Nice concise definitions of closures, map, fold, unfold and filter sneaked their way into the middle of a Dr. Dobbs article (via Raganwald):
Closures, are anonymous functions created at run-time which can refer to variables that are visible where the function is declared.
Closures are especially useful when performing operations over elements in a collection. The most common collection operations (aggregate operations) in functional programming are map, filter, fold, and unfold operations.
A map operation transforms a list into a new same-sized list by applying a transformation function (such as a closure) to each element in the original list. A common example of a map operation is when performing a vector scaling operation.
A filter operation creates a list from another list using only those items for which a predicate function returns true.
The fold operation combines values in a list using a binary function and an initial value. A summation function is a simple example of a fold operation.
The unfold operation creates a list from an initial value and by successively applying a generator function, until a terimination predicate returns true.
These are usually defined in much more obfuscated terms. It’s good to see them so clearly defined.
