Searles spends a good bit of time in Chapter 1 discussing tone and making sure to use a reader-centered perspective that utilizes a "you" approach and positive wording. In addition to a reader-centered perspective, however, you also should consider the difference between what is called a direct and an indirect approach when organizing letters, memos, and e-mails, especially ones that convey bad news. Searles mentions that letters, memo, and e-mails should have some kind of brief introduction, often as its own paragraph. If you're using the direct approach, this introduction is simply a straightforward statement of the main point of the message.
This section is written like a manual or guidebook. Please help rewrite this section from a descriptive, neutral point of viewand remove advice or instruction. April Learn how and when to remove this template message In CPS, each procedure takes an extra argument representing what should be done with the result the function is calculating.
This, along with a restrictive style prohibiting a variety of constructs usually available, is used to expose the semantics of programs, making them easier to analyze. The key to CPS is to remember that a every function takes an extra argument, its continuation, and b every argument in a function call must be either a variable or a lambda expression not a more complex expression.
This has the effect of turning expressions "inside-out" because the innermost parts of the expression must be evaluated first, so CPS explicates the order of evaluation as well as the control flow.
Some examples of code in direct style and the corresponding CPS appear below. These examples are written in the Scheme programming language ; by convention the continuation function is represented as a parameter named "k": There is some variety between compilers in the way primitive functions are provided in CPS.
The translations shown above show that CPS is a global transformation.
Any function calling a CPS-ed function must either provide a new continuation or pass its own; any calls from a CPS-ed function to a non-CPS function will use implicit continuations.
Thus, to ensure the total absence of a function stack, the entire program must be in CPS. CPS in Haskell [ edit ] In this section we will write a function that calculates hypotenuse using Pythagorean theorem. Traditional pyth function looks like this: Function will get another argument of function type and its return type depends on that function: And so on until we reach the result of our calculations.
To get the result of this function we can pass id function as a final argument which returns the value that was passed to it unchanged: This module provides Cont type, which implements Monad and some other useful functions. The following snippet shows pyth' function using Cont type: This function has the only argument of a function type; that function argument accepts the function too, which discards all computations going after its call.
For example let's break the execution of pyth function if at least one of its arguments is negative returning zero: Callback computer programming Programming with continuations can also be useful when a caller does not want to wait until the callee completes.
For example, in user-interface UI programming, a routine can set up dialog box fields and pass these, along with a continuation function, to the UI framework.
This call returns right away, allowing the application code to continue while the user interacts with the dialog box. Once the user presses the "OK" button, the framework calls the continuation function with the updated fields.
Although this style of coding uses continuations, it is not full CPS. The framework can execute the called function in a worker thread, then call the continuation function in the original thread with the worker's results.
This is in Java using the Swing UI framework: Using CPS without tail call optimization TCO will cause not only the constructed continuation to potentially grow during recursion, but also the call stack.
This is usually undesirable, but has been used in interesting ways—see the Chicken Scheme compiler. As CPS and TCO eliminate the concept of an implicit function return, their combined use can eliminate the need for a run-time stack.
Several compilers and interpreters for functional programming languages use this ability in novel ways.
Without tail-call optimization, techniques such as trampoliningi. Writing code in CPS, while not impossible, is often error-prone. There are various translations, usually defined as one- or two-pass conversions of pure lambda calculuswhich convert direct style expressions into CPS expressions.
Writing in trampolined style, however, is extremely difficult; when used, it is usually the target of some sort of transformation, such as compilation.
Functions using more than one continuation can be defined to capture various control flow paradigms, for example in Scheme: For example, within linguistic semanticsChris Barker and his collaborators have suggested that specifying the denotations of sentences using CPS might explain certain phenomena in natural language.
Accordingly, the result is obtained by passing the identity function as a continuation to the CPS-style expression, as in the above example. Classical logic itself relates to manipulating the continuation of programs directly, as in Scheme's call-with-current-continuation control operator, an observation due to Tim Griffin using the closely related C control operator.The Purdue University Online Writing Lab serves writers from around the world and the Purdue University Writing Lab helps writers on Purdue's campus.
Memos are characterized by being brief, direct, and easy to navigate.
They are less formal than letters but should maintain a professional, succinct style. Often, the purpose of a business memo is twofold: to identify a problem and propose a solution. * Memos have a direct style * Memos do not have a salutation * Memos do not have a complimentary closing to remember about good memo writing are as follows: * Remember memo format memo.
Edit Article How to Write a Formal Letter. In this Article: Article Summary Sample Formal Letters Writing a Traditional Block Style Letter Writing an AMS Style Letter Sending Your Letter Community Q&A Formal letters--They can shape others' perceptions of you, inform the reader of .
Sample Direct Memo. Sample Indirect Memo. Style and Tone. While memo reports and policy memos are examples of documents that have a more formal tone, most memos will have a conversational style—slightly informal but still professional. In a standard writing format, we might expect to see an introduction, a body, and a conclusion.
All these are present in a memo, and each part has a clear purpose. The declaration in the opening uses a declarative sentence to announce the main topic.