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[60] recover differs from catch in that it can only be called from within a defer code block in a function, so the handler can only do clean-up and change the function's return values, and cannot return control to an arbitrary point within the function. [61] The defer block itself functions similarly to a finally clause.
By returning a null object (i.e., an empty list) instead, there is no need to verify that the return value is in fact a list. The calling function may simply iterate the list as normal, effectively doing nothing. It is, however, still possible to check whether the return value is a null object (an empty list) and react differently if desired.
Common Lisp supports the concept of multiple values, [14] where any expression always has a single primary value, but it might also have any number of secondary values, which might be received and inspected by interested callers. This concept is distinct from returning a list value, as the secondary values are fully optional, and passed via a ...
[3] The precondition, and the definition of exception, is subjective. The set of "normal" circumstances is defined entirely by the programmer, e.g. the programmer may deem division by zero to be undefined, hence an exception, or devise some behavior such as returning zero or a special "ZERO DIVIDE" value (circumventing the need for exceptions). [4]
Mixins first appeared in Symbolics's object-oriented Flavors system (developed by Howard Cannon), which was an approach to object-orientation used in Lisp Machine Lisp.The name was inspired by Steve's Ice Cream Parlor in Somerville, Massachusetts: [1] The owner of the ice cream shop offered a basic flavor of ice cream (vanilla, chocolate, etc.) and blended in a combination of extra items (nuts ...
In C and C++, return exp; (where exp is an expression) is a statement that tells a function to return execution of the program to the calling function, and report the value of exp. If a function has the return type void, the return statement can be used without a value, in which case the program just breaks out of the current function and ...
Various techniques for returning multiple values include: Returning a tuple of values. This is conventional in languages (such as Python) that have a built-in tuple data type and special syntax for handling these: in Python, x, y = f() calls the function f returning a pair of values and assigns the elements of the pair to two variables.
Multiple dispatch or multimethods is a feature of some programming languages in which a function or method can be dynamically dispatched based on the run-time (dynamic) type or, in the more general case, some other attribute of more than one of its arguments. [1]