while in Java 9 it is planned to be large-scale, where a module is a collection of packages, which are in turn collections of files. Other terms for modules include unit, used in Pascal dialects. Language support Languages that formally support the module concept include Ada, Algol, BlitzMax, C++, C#, Clojure, COBOL, Common_Lisp, D, Dart, eC, Erlang, Elixir, Elm, F, F#, Fortran, Go, Haskell, IBM/360 Assembler, Control Language (CL), IBM RPG, Java, Julia, MATLAB, ML, Modula, Modula-2, Modula-3, Morpho, NEWP, Oberon, Oberon-2, Objective-C, OCaml, several derivatives of Pascal (Component Pascal, Object Pascal, Turbo Pascal, UCSD Pascal), Perl, PHP, PL/I, PureBasic, Python, R, Ruby, Rust, JavaScript, Visual Basic .NET and WebDNA. Conspicuous examples of languages that lack support for modules are C and have been C++ and Pascal in their original form, C and C++ do, however, allow separate compilation and declarative interfaces to be specified using header files. Modules were added to Objective-C in iOS 7 (2013); to C++ with C++20, and Pascal was superseded by Modula and Oberon, which included modules from the start, and various derivatives that included modules. JavaScript has had native modules since ECMAScript 2015. Modular programming can be performed even where the programming language lacks explicit syntactic features to support named modules, like, for example, in C. This is done by using existing language features, together with, for example, coding conventions, programming idioms and the physical code structure. IBM i also uses modules when programming in the Integrated Language Environment (ILE). Key aspects With modular programming, concerns are separated such that modules perform logically discrete functions, interacting through well-defined interfaces. Often modules form a directed acyclic graph (DAG); in this case a cyclic dependency between modules is seen as indicating that these should be a single module. In the case where modules do form a DAG they can be arranged as a hierarchy, where the lowest-level modules are independent, depending on no other modules, and higher-level modules depend on lower-level ones. A particular program or library is a top-level module of its own hierarchy, but can in turn be seen as a lower-level module of a higher-level program, library, or system. When creating a modular system, instead of creating a monolithic application (where the smallest component is the whole), several smaller modules are written separately so when they are composed together, they construct the executable application program. Typically, these are also compiled separately, via separate