353 research outputs found
Polymonadic Programming
Monads are a popular tool for the working functional programmer to structure
effectful computations. This paper presents polymonads, a generalization of
monads. Polymonads give the familiar monadic bind the more general type forall
a,b. L a -> (a -> M b) -> N b, to compose computations with three different
kinds of effects, rather than just one. Polymonads subsume monads and
parameterized monads, and can express other constructions, including precise
type-and-effect systems and information flow tracking; more generally,
polymonads correspond to Tate's productoid semantic model. We show how to equip
a core language (called lambda-PM) with syntactic support for programming with
polymonads. Type inference and elaboration in lambda-PM allows programmers to
write polymonadic code directly in an ML-like syntax--our algorithms compute
principal types and produce elaborated programs wherein the binds appear
explicitly. Furthermore, we prove that the elaboration is coherent: no matter
which (type-correct) binds are chosen, the elaborated program's semantics will
be the same. Pleasingly, the inferred types are easy to read: the polymonad
laws justify (sometimes dramatic) simplifications, but with no effect on a
type's generality.Comment: In Proceedings MSFP 2014, arXiv:1406.153
Linear Haskell: practical linearity in a higher-order polymorphic language
Linear type systems have a long and storied history, but not a clear path
forward to integrate with existing languages such as OCaml or Haskell. In this
paper, we study a linear type system designed with two crucial properties in
mind: backwards-compatibility and code reuse across linear and non-linear users
of a library. Only then can the benefits of linear types permeate conventional
functional programming. Rather than bifurcate types into linear and non-linear
counterparts, we instead attach linearity to function arrows. Linear functions
can receive inputs from linearly-bound values, but can also operate over
unrestricted, regular values.
To demonstrate the efficacy of our linear type system - both how easy it can
be integrated in an existing language implementation and how streamlined it
makes it to write programs with linear types - we implemented our type system
in GHC, the leading Haskell compiler, and demonstrate two kinds of applications
of linear types: mutable data with pure interfaces; and enforcing protocols in
I/O-performing functions
In the Age of Web: Typed Functional-First Programming Revisited
Most programming languages were designed before the age of web. This matters
because the web changes many assumptions that typed functional language
designers take for granted. For example, programs do not run in a closed world,
but must instead interact with (changing and likely unreliable) services and
data sources, communication is often asynchronous or event-driven, and programs
need to interoperate with untyped environments.
In this paper, we present how the F# language and libraries face the
challenges posed by the web. Technically, this comprises using type providers
for integration with external information sources and for integration with
untyped programming environments, using lightweight meta-programming for
targeting JavaScript and computation expressions for writing asynchronous code.
In this inquiry, the holistic perspective is more important than each of the
features in isolation. We use a practical case study as a starting point and
look at how F# language and libraries approach the challenges posed by the web.
The specific lessons learned are perhaps less interesting than our attempt to
uncover hidden assumptions that no longer hold in the age of web.Comment: In Proceedings ML/OCaml 2014, arXiv:1512.0143
EbbRT: a framework for building per-application library operating systems
Efficient use of high speed hardware requires operating system components be customized to the application work- load. Our general purpose operating systems are ill-suited for this task. We present EbbRT, a framework for constructing per-application library operating systems for cloud applications. The primary objective of EbbRT is to enable high-performance in a tractable and maintainable fashion. This paper describes the design and implementation of EbbRT, and evaluates its ability to improve the performance of common cloud applications. The evaluation of the EbbRT prototype demonstrates memcached, run within a VM, can outperform memcached run on an unvirtualized Linux. The prototype evaluation also demonstrates an 14% performance improvement of a V8 JavaScript engine benchmark, and a node.js webserver that achieves a 50% reduction in 99th percentile latency compared to it run on Linux
On Role Logic
We present role logic, a notation for describing properties of relational
structures in shape analysis, databases, and knowledge bases. We construct role
logic using the ideas of de Bruijn's notation for lambda calculus, an encoding
of first-order logic in lambda calculus, and a simple rule for implicit
arguments of unary and binary predicates. The unrestricted version of role
logic has the expressive power of first-order logic with transitive closure.
Using a syntactic restriction on role logic formulas, we identify a natural
fragment RL^2 of role logic. We show that the RL^2 fragment has the same
expressive power as two-variable logic with counting C^2 and is therefore
decidable. We present a translation of an imperative language into the
decidable fragment RL^2, which allows compositional verification of programs
that manipulate relational structures. In addition, we show how RL^2 encodes
boolean shape analysis constraints and an expressive description logic.Comment: 20 pages. Our later SAS 2004 result builds on this wor
Koka: Programming with Row Polymorphic Effect Types
We propose a programming model where effects are treated in a disciplined
way, and where the potential side-effects of a function are apparent in its
type signature. The type and effect of expressions can also be inferred
automatically, and we describe a polymorphic type inference system based on
Hindley-Milner style inference. A novel feature is that we support polymorphic
effects through row-polymorphism using duplicate labels. Moreover, we show that
our effects are not just syntactic labels but have a deep semantic connection
to the program. For example, if an expression can be typed without an exn
effect, then it will never throw an unhandled exception. Similar to Haskell's
`runST` we show how we can safely encapsulate stateful operations. Through the
state effect, we can also safely combine state with let-polymorphism without
needing either imperative type variables or a syntactic value restriction.
Finally, our system is implemented fully in a new language called Koka and has
been used successfully on various small to medium-sized sample programs ranging
from a Markdown processor to a tier-splitted chat application. You can try out
Koka live at www.rise4fun.com/koka/tutorial.Comment: In Proceedings MSFP 2014, arXiv:1406.153
EbbRT: a customizable operating system for cloud applications
Efficient use of hardware requires operating system components be customized to the application workload. Our general purpose operating systems are ill-suited for this task. We present Genesis, a new operating system that enables per-application customizations for cloud applications. Genesis achieves this through a novel heterogeneous distributed structure, a partitioned object model, and an event-driven execution environment. This paper describes the design and prototype implementation of Genesis, and evaluates its ability to improve the performance of common cloud applications. The evaluation of the Genesis prototype demonstrates memcached, run within a VM, can outperform memcached run on an unvirtualized Linux. The prototype evaluation also demonstrates an 14% performance improvement of a V8 JavaScript engine benchmark, and a node.js webserver that achieves a 50% reduction in 99th percentile latency compared to it run on Linux
A functional approach to heterogeneous computing in embedded systems
Developing programs for embedded systems presents quite a challenge; not only should programs be resource efficient, as they operate under memory and timing constraints, but they should also take full advantage of the hardware to achieve maximum performance. Since performance is such a significant factor in the design of embedded systems, modern systems typically incorporate more than one kind of processing element to benefit from specialized processing capabilities. For such heterogeneous systems the challenge in developing programs is even greater.In this thesis we explore a functional approach to heterogeneous system development as a means to address many of the modularity problems that are typically found in the application of low-level imperative programming for embedded systems. In particular, we explore a staged hardware software co-design language that we name Co-Feldspar and embed in Haskell. The staged approach enables designers to build their applications from reusable components and skeletons while retaining control over much of the generated source code. Furthermore, by embedding the language in Haskell we can exploit its type classes to write not only hardware and software programs, but also generic programs with overloaded instructions and expressions. We demonstrate the usefulness of the functional approach for co-design on a cryptographic example and signal processing filters, and benchmark software and mixed hardware-software implementations. Co-Feldspar currently adopts a monadic interface, which provides an imperative functional programming style that is suitable for explicit memory management and algorithms that rely on a certain evaluation order. For algorithms that are better defined as pure functions operating on immutable values, we provide a signal and array library that extends a monadic language, like Co-Feldspar. These extensions permit a functional style of programming by composing high-level combinators. Our compiler transforms such high-level code into efficient programs with mutating code. In particular, we show how to execute an FFT safely in-place, and how to describe a FIR and IIR filter efficiently as streams. Co-Feldspar’s monadic interface is however quite invasive; not only is the burden of explicit memory management quite heavy on the user, it is also quite easy to shoot on eself in the foot. It is for these reasons that we also explore a dynamic memory management discipline that is based on regions but predictable enough to be of use for embedded systems. Specifically, this thesis introduces a program analysis which annotates values with dynamically allocated memory regions. By limiting our efforts to functional languages that target embedded software, we manage to define a region inference algorithm that is considerably simpler than traditional approaches
- …