3.5 Error Checking in Function Calls
3.5.1 Argument Mismatch Detection
3.5.1.1 Safe and Unsafe Calls
A call is a safe call if each of the following is either safe code or system code (other than system code that results from macro expansion of programmer code):
• the call.
• the definition of the function being called.
• the point of functional evaluation
The following special cases require some elaboration:
• If the function being called is a generic function, it is considered safe if all of the following are safe code or system code:
– its definition (if it was defined explicitly).
– the method definitions for all applicable methods.
– the definition of its method combination.
• For the form (coerce x ’function), where x is a lambda expression, the value of the optimize quality safety in the global environment at the time the coerce is executed applies to the resulting function.
• For a call to the function ensure-generic-function, the value of the optimize quality safety in the environment object passed as the :environment argument applies to the resulting generic function.
• For a call to compile with a lambda expression as the argument, the value of the optimize quality safety in the global environment at the time compile is called applies to the resulting compiled function.
• For a call to compile with only one argument, if the original definition of the function was safe, then the resulting compiled function must also be safe.
• A call to a method by call-next-method must be considered safe if each of the following is safe code or system code:
– the definition of the generic function (if it was defined explicitly).
– the method definitions for all applicable methods.
– the definition of the method combination.
– the point of entry into the body of the method defining form, where the binding of call-next-method is established.
– the point of functional evaluation of the name call-next-method.
An unsafe call is a call that is not a safe call.
The informal intent is that the programmer can rely on a call to be safe, even when system code is involved, if all reasonable steps have been taken to ensure that the call is safe. For example, if a programmer calls mapcar from safe code and supplies a function that was compiled as safe, the implementation is required to ensure that mapcar makes a safe call as well.
3.5.1.1.1 Error Detection Time in Safe Calls
If an error is signaled in a safe call, the exact point of the signal is implementation-dependent. In particular, it might be signaled at compile time or at run time, and if signaled at run time, it might be prior to, during, or after executing the call. However, it is always prior to the execution of the body of the function being called.
3.5.1.2 Too Few Arguments
It is not permitted to supply too few arguments to a function. Too few arguments means fewer arguments than the number of required parameters for the function.
If this situation occurs in a safe call, an error of type program-error must be signaled; and in an unsafe call the situation has undefined consequences.
3.5.1.3 Too Many Arguments
It is not permitted to supply too many arguments to a function. Too many arguments means more arguments than the number of required parameters plus the number of optional parameters; however, if the function uses &rest or &key, it is not possible for it to receive too many arguments.
If this situation occurs in a safe call, an error of type program-error must be signaled; and in an unsafe call the situation has undefined consequences.
3.5.1.4 Unrecognized Keyword Arguments
It is not permitted to supply a keyword argument to a function using a name that is not recognized by that function unless keyword argument checking is suppressed as described in Section 3.4.1.4.1 (Suppressing Keyword Argument Checking).
If this situation occurs in a safe call, an error of type program-error must be signaled; and in an unsafe call the situation has undefined consequences.
3.5.1.5 Invalid Keyword Arguments
It is not permitted to supply a keyword argument to a function using a name that is not a symbol.
If this situation occurs in a safe call, an error of type program-error must be signaled unless keyword argument checking is suppressed as described in Section 3.4.1.4.1 (Suppressing Keyword Argument Checking); and in an unsafe call the situation has undefined consequences.
3.5.1.6 Odd Number of Keyword Arguments
An odd number of arguments must not be supplied for the keyword parameters.
If this situation occurs in a safe call, an error of type program-error must be signaled unless keyword argument checking is suppressed as described in Section 3.4.1.4.1 (Suppressing Keyword Argument Checking); and in an unsafe call the situation has undefined consequences.
3.5.1.7 Destructuring Mismatch
When matching a destructuring lambda list against a form, the pattern and the form must have compatible tree structure, as described in Section 3.4.4 (Macro Lambda Lists).
Otherwise, in a safe call, an error of type program-error must be signaled; and in an unsafe call the situation has undefined consequences.
3.5.1.8 Errors When Calling a Next Method
If call-next-method is called with arguments, the ordered set of applicable methods for the changed set of arguments for call-next-method must be the same as the ordered set of applicable methods for the original arguments to the generic function, or else an error should be signaled.
The comparison between the set of methods applicable to the new arguments and the set applicable to the original arguments is insensitive to order differences among methods with the same specializers.
If call-next-method is called with arguments that specify a different ordered set of applicable methods and there is no next method available, the test for different methods and the associated error signaling (when present) takes precedence over calling no-next-method.