Protecting confidentiality of data has become increasingly important for computing systems. Information-flow techniques have been developed over the years to achieve that purpose, leading to special-purpose languages that guarantee information-flow security in programs. However, rather than producing a new language from scratch, information-flow security can also be provided as a library. This has been done previously in Haskell using the arrow framework. In this paper, we show that arrows are not necessary to design such libraries and that a less general notion, namely monads, is sufficient to achieve the same goals. We present a monadic library to provide information-flow security for Haskell programs. The library introduces mechanisms to protect confidentiality of data for pure computations, that we then easily, and modularly, extend to include dealing with side-effects. We also present combinators to dynamically enforce different declassification policies when release of information is required in a controlled manner. It is possible to enforce policies related to what, by whom, and when information is released or a combination of them. The well-known concept of monads together with the light-weight characteristic of our approach makes the library suitable to build applications where confidentiality of data is an issue.
We address the problem of testing and debugging concurrent, distributed Erlang applications. In concurrent programs, race conditions are a common class of bugs and are very hard to find in practice. Traditional unit testing is normally unable to help finding all race conditions, because their occurrence depends so much on timing. Therefore, race conditions are often found during system testing, where due to the vast amount of code under test, it is often hard to diagnose the error resulting from race conditions. We present three tools (QuickCheck, PULSE, and a visualizer) that in combination can be used to test and debug concurrent programs in unit testing with a much better possibility of detecting race conditions. We evaluate our method on an industrial concurrent case study and illustrate how we find and analyze the race conditions.
In this paper we describe the implementation of several graphical programming paradigms (Model View Controller, Fudgets, and Fimctional Animations) uaing the GUI library TkGofer. This library relies on a combination of monads and multiple-parameter type classes to provide an abstract, type safe interface to Tcl/Tk.We show how choosing the right abstractions makes the given implementations surprisingly concise and easy to understand.
We propose a new programming model for web applications which is (1) seamless; one program and one language is used to produce code for both client and server, (2) client-centric; the programmer takes the viewpoint of the client that runs code on the server rather than the other way around, (3) functional and type-safe, and (4) portable; everything is implemented as a Haskell library that implicitly takes care of all networking code. Our aim is to improve the painful and error-prone experience of today's standard development methods, in which clients and servers are coded in different languages and communicate with each other using ad-hoc protocols. We present the design of our library called Haste.App, an example web application that uses it, and discuss the implementation and the compiler technology on which it depends.
We present a divide-and-conquer algorithm for parsing context-free languages efficiently. Our algorithm is an instance of Valiant's (1975), who reduced the problem of parsing to matrix multiplications. We show that, while the conquer step of Valiant's is O ( n 3 ) in the worst case, it improves to O (log n 3 ), under certain conditions satisfied by many useful inputs. These conditions occur for example in program texts written by humans. The improvement happens because the multiplications involve an overwhelming majority of empty matrices. This result is relevant to modern computing: divide-and-conquer algorithms can be parallelized relatively easily.
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