Amber
نویسنده
چکیده
Introduction The Amber language embeds many recent ideas in programming language design, and tries to introduce all the features in their minimal, essential, form. One of its main goals is to safely blend static typing with the dynamic requirements of a system programming language. For this purpose, multiple inheritance and persistent objects are integrated in a strongly typed language. Other features include graphics, higher-order functions, modules and concurrency. Amber is a spin-off of the ML programming language [Milner 84]. The ML language is now being standardized, and as such is not very suitable for experimentation. Amber is intended as a tool for trying out new ideas in language implementation, language design, and language environments, while being deeply influenced by the ML experience. As a programming language, Amber was defined to experiment with a new style of polymorphism [Cardelli 84b] which, unlike the ML-style parametric polymorphism [Milner 78], is based on a notion of type inclusion, and can be used to interpret many programming concepts found in object-oriented languages [Goldberg Robson 83]. In this view, the main features of functional and object-oriented languages can be naturally integrated, and the combination of higher-order functions and multiple inheritance can be strongly typed. Some typechecking anomalies are still present in Amber, and current research is aimed at solving them and integrating inclusion polymorphism with parametric polymorphism. Type inclusion also plays an important role in modularization. Amber programs can be partitioned into modules and separately compiled. Modules have import-export lists for types and values. When a type is imported, its actual definition is not accessible: this is a form of data abstraction realized through the module mechanism, and implies that modules can be compiled in any order. It is possible to specify that two imported types, although unknown, are one a subtype of the other, so that inheritance can be made to work across module boundaries. At the programming system level, the implementation is heavily based on the ability to export and import arbitrary values to/from persistent storage. This feature is provided at the lowest level, and guarantees the preservation of any circularity or sharing present in the
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