Multicellular organisms utilize cell-to-cell signals to build patterns of cell types within embryos, but the ability of fungi to form organized communities has been largely unexplored. Here we report that colonies of the yeast Saccharomyces cerevisiae formed sharply divided layers of sporulating and nonsporulating cells. Sporulation initiated in the colony's interior, and this region expanded upward as the colony matured. Two key activators of sporulation, IME1 and IME2, were initially transcribed in overlapping regions of the colony, and this overlap corresponded to the initial sporulation region. The development of colony sporulation patterns depended on cell-to-cell signals, as demonstrated by chimeric colonies, which contain a mixture of two strains. One such signal is alkaline pH, mediated through the Rim101p/PacC pathway. Meiotic-arrest mutants that increased alkali production stimulated expression of an early meiotic gene in neighboring cells, whereas a mutant that decreased alkali production (cit1D) decreased this expression. Addition of alkali to colonies accelerated the expansion of the interior region of sporulation, whereas inactivation of the Rim101p pathway inhibited this expansion. Thus, the Rim101 pathway mediates colony patterning by responding to cell-to-cell pH signals. Cell-to-cell signals coupled with nutrient gradients may allow efficient spore formation and spore dispersal in natural environments.

There has been much recent interest in adopting functional and reactive programming for use in real-time system design. Moving toward a more declarative methodology for developing real-time systems purports to improve the fidelity of software. To study the benefits of functional and reactive programming for real-time systems, real-time aware functional compilers and language runtimes are required. In this paper we examine the necessary changes to a modern Standard ML compiler, MLton, to provide basic support for real-time execution. We detail our current progress in modifying MLton with a threading model that supports priorities, a chunked object model to support real-time garbage collection, and low level modification to execute on top of a real-time operating system. We present preliminary numbers and our work in progress prototype, which is able to boot ML programs compiled with MLton on x86 machines.

Functional programming languages play an important role in the development of correct software systems. As embedded devices become pervasive and perform critical tasks in our lives, their reliability becomes paramount. This presents a natural opportunity to explore the application of functional programming languages to systems that demand highly predictable behavior.In this paper, we explore existing functional programming language compilers and their applicability to real-time embedded systems. We do this by defining important characteristics needed by a real-time programming language and survey how well existing languages meet these characteristics. We conduct empirical analysis of language runtimes in order to assess the impact of dynamic memory management on predictability and performance. Lastly, we review different programming models for expressing real-time considerations in applications. INTRODUCTIONReal-time software is an integral part in many complex software/hardware systems that require timing guarantees in addition to traditional functional correctness guarantees. Such systems vary in nature, spanning multiple domains including industrial control, robotics, automotive, avionics, and medical devices, among others. These systems all provide services whose utility is dictated by the timeliness in which they respond to external (eg, sensor readings) and internal (eg, software events and interrupts) stimuli. Writing the software for these systems is a difficult undertaking because ensuring the system is correct requires providing predictability guarantees. This is exacerbated by the fact that most software for real-time systems is written in "low level" imperative languages.Functional languages are known for their ability to be reasoned about with respect to correctness, often with automated tools. 1-3 Given that real-time systems are frequently deployed in safety-critical and mission-critical situations, the ability to write software with a high degree of confidence in its correctness and predictability is important. Functional languages are well suited for the former task (correctness), but are not developed for the latter (predictability). Indeed, general purpose, functional programming languages are not used for developing real-time systems and there are no investigations to ensure their predictability. There are, however, many domain-specific functional languages that provide predictability for niche domains. The state of mainstream functional programming languages with respect to their ability to express and provide predictability is something we would like to investigate in this survey.One reason that functional languages are not considered for writing real-time software is because they are managed languages and automatic memory management has classically been considered unpredictable. While many may consider this a reason to reject functional programming as a target language for real-time systems development, we can instead look to managed object-oriented systems for inspiration. Indeed, the ques...