iTasks for a change

Abstract

Workflow management systems (WFMS) are software systems that coordinate the tasks human workers and computers have to perform to achieve a certain goal based on a given workflow description. Due to changing circumstances, it happens often that some tasks in a running workflow need to be performed differently than originally planned and specified. Most commercial WFMSs cannot deal with the required run-time changes properly. These changes have to be specified at the level of the underlying Petri-Net based semantics. Moreover, the implicit external state has to be adapted to the new task as well. Such low-level updates can easily lead to wrong behaviour and other errors. This problem is known as the dynamic change bug. In the iTask WFMS, workflows are specified using a radically different approach: workflows are constructed in a compositional style, using pure functions and combinators as selfcontained building blocks. This paper introduces a change concept for the iTask system where self-contained tasks can be replaced by other self-contained tasks, thereby preventing dynamic change bugs. The static and dynamic typing system furthermore guarantees that these tasks have compatible types.

Multitasking on Microcontrollers using Task Oriented Programming

“…They will be explained on demand with the examples. All details regarding the exact types and the actual class definitions can be found in the repository 2 .…”

“…They function as lightweight communicating threads and can be automatically interleaved because the work is inherently divided up into small rewrite steps. A programming language providing TOP for the web is iTasks [1], an eDSL hosted in Clean [2]. Data can be safely shared between tasks using Shared Data Sources (SDSs).…”

Defining Multi-user Web Applications with iTasks

“…It comes with an interpreter that has competitive performance when compared with other functional language interpreters such as Hugs, Helium, GHCi, and Amanda. -Workflows being executed can be changed while the work is going on [17].…”

“…-Tasks can become web applications including GUI elements like buttons, dialogues, windows and menus [15]. -The semantics of iTask combinators has been formally described [11,17].…”

Embedding polymorphic dynamic typing

“…Then, a value is unwrapped using the library function fromDyn which performs a cast, where the required type is specified by the context in which it is unwrapped: inc :: Maybe (Int → Int) inc = fromDyn incDyn Clean, on the other hand, has a more rich and mature dynamic typing system that is built in; it adopted ML's support for monomorphism (Abadi et al, 1991;Pil, 1997) and polymorphism (Abadi et al, 1994;Leroy and Mauny, 1993). Having such an extensive dynamic typing system does not only improve orthogonality with the static typing system (Van Noort et al, 2010), but also has important applications (Plasmeijer and Van Weelden, 2005;Plasmeijer et al, 2011). In Clean, we wrap a value, for example the polymorphic identity function, in a dynamic by using the corresponding keyword:…”