Execution of code can be accomplished by a variety of means ranging from direct interpretation of a form representing a program to invocation of compiled code produced by a compiler.
Evaluation is the process by which a program is executed in Common Lisp.
The mechanism of evaluation is manifested
both implicitly through the effect of the Lisp read-eval-print loop,
and explicitly through the presence of the functions
eval,
compile,
compile-file,
and load.
Any of these facilities might share the same execution strategy,
or each might use a different one.
The behavior of a conforming program processed by eval
and by compile-file might differ; see Section 3.2.2.3 (Semantic Constraints).
Evaluation can be understood in terms of a model in which an interpreter recursively traverses a form performing each step of the computation as it goes. This model, which describes the semantics of Common Lisp programs, is described in Section 3.1.2 (The Evaluation Model).