Page "Programming language" Paragraph 57

A language's core library is often treated as part of the language by its users, although the designers may have treated it as a separate entity.

Many language specifications define a core that must be made available in all implementations, and in the case of standardized languages this core library may be required.

The line between a language and its core library therefore differs from language to language.

Indeed, some languages are designed so that the meanings of certain syntactic constructs cannot even be described without referring to the core library.

For example, in Java, a string literal is defined as an instance of the < tt > java. lang. String </ tt > class ; similarly, in Smalltalk, an anonymous function expression ( a " block ") constructs an instance of the library's < tt > BlockContext </ tt > class.

Conversely, Scheme contains multiple coherent subsets that suffice to construct the rest of the language as library macros, and so the language designers do not even bother to say which portions of the language must be implemented as language constructs, and which must be implemented as parts of a library.