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For example, a function may retrieve a list of files in a folder and perform some action on each. In the case of an empty folder, one response may be to throw an exception or return a null reference rather than a list. Thus, the code expecting a list must verify that it in fact has one before continuing, which can complicate the design.
Example one shows how narrative text can be interspersed with testable examples in a docstring. In the second example, more features of doctest are shown, together with their explanation. Example three is set up to run all doctests in a file when the file is run, but when imported as a module, the tests will not be run.
Folds can be regarded as consistently replacing the structural components of a data structure with functions and values. Lists, for example, are built up in many functional languages from two primitives: any list is either an empty list, commonly called nil ([]), or is constructed by prefixing an element in front of another list, creating what is called a cons node ( Cons(X1,Cons(X2,Cons ...
The list starts out with a single node, the sentinel node which has the next and previous pointers point to itself. This condition determines if the list is empty. In a non-empty list, the sentinel node's next pointer gives the head of the list, and the previous pointer gives the tail of the list.
Use the ; empty statement [10] or the {} empty block statement the same way as in the C and derivatives examples; Use the undefined or the null expression as a complete statement (an expression statement) when the previous methods are not allowed by the syntax. Alternatives, in situations where a function is required, are:
The most important basic example of this is a tree, which can be defined mutually recursively in terms of a forest (a list of trees). Symbolically: f: [t[1], ..., t[k]] t: v f A forest f consists of a list of trees, while a tree t consists of a pair of a value v and a forest f (its children). This definition is elegant and easy to work with ...
This discussion will be technical, so recall that, for a list, | | denotes its length, that NIL represents an empty list and (,) represents the list whose head is h and whose tail is t. The data structure used to implement our queues consists of three singly-linked lists ( f , r , s ) {\displaystyle (f,r,s)} where f is the front of the ...
Property list files use the filename extension.plist, and thus are often referred to as p-list files. Property list files are often used to store a user's settings. They are also used to store information about bundles and applications , a task served by the resource fork in the old Mac OS.