This paper shows how type effect systems can be combined with model-checking techniques to produce powerful, automatically verifiable program logics for higher-order programs. The properties verified are based on the ordered sequence of events that occur during program execution-an event history. Our type and effect systems automatically infer conservative approximations of the event histories arising at run-time, and model-checking techniques are used to verify logical properties of these histories. Our language model is based on the λ-calculus. Technical results include a powerful type inference algorithm for a polymorphic type effect system, and a method for applying known model-checking techniques to the history effects inferred by the type inference algorithm, allowing static enforcement of history-and stackbased security mechanisms.

Abstract. The Java JDK 1.2 Security Architecture includes a dynamic mechanism for enforcing access control checks, so-called stack inspection. This paper studies type systems which can statically guarantee the success of these checks. We develop these systems using a new, systematic methodology: we show that the security-passing style translation, proposed by Wallach and Felten as a dynamic implementation technique, also gives rise to static security-aware type systems, by composition with conventional type systems. To define the latter, we use the general HM(X) framework, and easily construct several constraint-and unification-based type systems. They offer significant improvements on a previous type system for JDK access control, both in terms of expressiveness and in terms of readability of inferred type specifications.

BackgroundVictims of trauma are at high risk for mental health conditions such as posttraumatic stress disorder and depression. Regular assessment of mental health symptoms in the post-trauma period is necessary to identify those at greatest risk and provide treatment. The multiple demands of the acute post-trauma period present numerous barriers to such assessments. Mobile apps are a method by which to overcome these barriers in order to regularly assess symptoms, identify those at risk, and connect patients to needed services.ObjectiveThe current study conducted a usability evaluation of a system to monitor mental health symptoms after a trauma. The system was developed to promote ease of use and facilitate quick transmission of data.MethodsA sample of 21 adults with a history of trauma completed a standardized usability test in a laboratory setting followed by a qualitative interview.ResultsUsability testing indicated that the app was easy to use and that patients were able to answer several questions in less than 1 minute (mean [SD] 29.37 [7.53]; range 15-57). Qualitative analyses suggested that feedback should be included in such an app and recommendations for the type of feedback were offered.ConclusionsThe results of the current study indicate that a mobile app to monitor post-trauma mental health symptoms would be well received by victims. Personalized feedback to the user was identified as critical to promote the usability of the software.

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Abstract. This paper shows how type effect systems can be combined with model-checking techniques to produce powerful, automatically verifiable program logics for higher order programs. The properties verified are based on the ordered sequence of events that occur during program execution, so called event traces. Our type and effect systems infer conservative approximations of the event traces arising at run-time, and model-checking techniques are used to verify logical properties of these histories. Our language model is based on the λ-calculus. Technical results include a type inference algorithm for a polymorphic type effect system, and a method for applying known model-checking techniques to the trace effects inferred by the type inference algorithm, allowing static enforcement of history-and stack-based security mechanisms. A type safety result is proven for both unification and subtyping constraint versions of the type system, ensuring that statically well-typed programs do not contain trace event checks that can fail at run-time.