Direct definition

Direct definition may refer to any of several different function styles, which share the feature that arguments are given default names rather than having names defined in a header:
 * Direct definition (notation), a named style defined by Ken Iverson and used to discuss APL in the 1970s and 80s
 * Direct definition (operator), an anonymous function produced in NARS by applying  to strings
 * Direct Definition, a J form that simplifies explicit function syntax to define anonymous functions
 * "Direct function" is one expansion of dfn, an anonymous function style introduced by Dyalog APL and written with curly braces.