Compiler Terminology (ANSI and GNU Common Lisp Document)

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#### 3.2.1 Compiler Terminology

The following terminology is used in this section.

The compiler is a utility that translates code into an implementation-dependent form that might be represented or executed efficiently. The term compiler refers to both of the functions compile and compile-file.

The term compiled code refers to objects representing compiled programs, such as objects constructed by compile or by load when loading a compiled file.

The term implicit compilation refers to compilation performed during evaluation.

The term literal object refers to a quoted object or a self-evaluating object or an object that is a substructure of such an object. A constant variable is not itself a literal object.

The term coalesce is defined as follows. Suppose `A` and `B` are two literal constants in the source code, and that `A'` and `B'` are the corresponding objects in the compiled code. If `A'` and `B'` are eql but `A` and `B` are not eql, then it is said that `A` and `B` have been coalesced by the compiler.

The term minimal compilation refers to actions the compiler must take at compile time. These actions are specified in Compilation Semantics.

The verb process refers to performing minimal compilation, determining the time of evaluation for a form, and possibly evaluating that form (if required).

The term further compilation refers to implementation-dependent compilation beyond minimal compilation. That is, processing does not imply complete compilation. Block compilation and generation of machine-specific instructions are examples of further compilation. Further compilation is permitted to take place at run time.

Four different environments relevant to compilation are distinguished: the startup environment, the compilation environment, the evaluation environment, and the run-time environment.

The startup environment is the environment of the Lisp image from which the compiler was invoked.

The compilation environment is maintained by the compiler and is used to hold definitions and declarations to be used internally by the compiler. Only those parts of a definition needed for correct compilation are saved. The compilation environment is used as the environment argument to macro expanders called by the compiler. It is unspecified whether a definition available in the compilation environment can be used in an evaluation initiated in the startup environment or evaluation environment.

The evaluation environment is a run-time environment in which macro expanders and code specified by eval-when to be evaluated are evaluated. All evaluations initiated by the compiler take place in the evaluation environment.

The run-time environment is the environment in which the program being compiled will be executed.

The compilation environment inherits from the evaluation environment, and the compilation environment and evaluation environment might be identical. The evaluation environment inherits from the startup environment, and the startup environment and evaluation environment might be identical.

The term compile time refers to the duration of time that the compiler is processing source code. At compile time, only the compilation environment and the evaluation environment are available.

The term compile-time definition refers to a definition in the compilation environment. For example, when compiling a file, the definition of a function might be retained in the compilation environment if it is declared inline. This definition might not be available in the evaluation environment.

The term run time refers to the duration of time that the loader is loading compiled code or compiled code is being executed. At run time, only the run-time environment is available.

The term run-time definition refers to a definition in the run-time environment.

The term run-time compiler refers to the function compile or implicit compilation, for which the compilation and run-time environments are maintained in the same Lisp image. Note that when the run-time compiler is used, the run-time environment and startup environment are the same.

Next: Compilation Semantics, Previous: Compilation, Up: Compilation