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The OPTIMIZE declaration includes three concepts: DEBUG, SPEED, SAFETY and SPACE. Each of these declarations can take one of the integer values 0, 1, 2 and 3. According to these values, the implementation may decide how to compie or interpret a given lisp form. &ECL; currently does not use all these declarations, but some of them definitely affect the speed and behavior of compiled functions. For instance, the DEBUG declaration, as shown in , if the value of debugging is zero, the function will not appear in the debugger and, if redefined, some functions might not see the redefinition. Behavior 0 1 2 3 Compiled functions in the same source file are called directly Y Y N N Compiled function appears in debugger backtrace N N Y Y All functions get a global entry, that is, SI:C-LOCAL is ignored. N N Y Y A bit more critical is the value of SAFETY because as shown in Table , it may affect the safety checks generated by the compiler. In particular, in some circumstances the compiler may assume that the arguments to a function are properly typed. For instance, if you compile with a low value of SAFETY, and invoke RPLACA, the consequences are unspecified. Behavior 0 1 2 3 The compiler generates type checks for the arguments of a lambda form, thus enforcing any type declaration written by the user. N Y Y Y The value of an expression or a variable declared by the user is assumed to be right. Y Y N N We believe type declarations and type inference and, if the type of a form is inferred to be right for a function, slot accessor, etc, this may be inlined. Affects functions like CAR, CDR, etc Y Y N N We believe types defined before compiling a file not change before the compiled code is loaded. Y Y N N Arguments in a lisp form are assumed to have the appropriate types so that the form will not fail. Y N N N The slots or fields in a lisp object are accessed directly without type checks even if the type of the object could not be inferred (see line above). Affects functions like PATHNAME-TYPE, CAR, REST, etc. Y N N N