Basics of Using vp, a Value-Pasing Front End for the Concurrency Workbench

These notes describe some of the basics of using Glenn Bruns’ vp [1], which is a valuepassing front-end for the Concurrency Workbench [3]. The official documentation is available at http://www.bell-labs.com/user/grb/vp/vp.html, but it is fairly cryptic to the uninitiated. These notes are intended to fill in some of the gaps. 1 Running vp An overview of Glenn Bruns’ value-passing front end for the Concurrency Workbench is available at http://www.bell-labs.com/user/grb/vp/vp.html. In particular, that web page includes pointers to a (postscript) user’s guide [1] and the definition of value-passing CCS [2]. Running vp on the ECS Unix system is very simple: 1. Create a file with your definitions (see the rest of this writeup for more details). Make sure that the extension is .vp. For the rest of these instructions, imagine that the file is example.vp. 2. Run the following command at the Unix prompt (notice the .vp extension is not included): vp example 3. The result (if all goes well) is a file example.ccs that contains code that the Concurrency Workbench can handle. 2 Basic Components of Syntax 2.1 Constants Constants serve the purpose that constants usually serve in a programming language: they support abstraction and a more elegant coding style. They are especially useful for defining sets that will be used to index or parameterize actions and processes. Here are some sample constant declarations: const I = {1,2} const n = 5 const A = {2,4,6} Notice that, unlike CWB notation, these commands do not terminate with semi-colons. 1 2.2 Parameterized labels Parameterized labels are defined using the following syntax: label b(I) The result of this command is to create a channel b that accepts/passes values from the set I. The action corresponding to receiving a value on channel b is written as follows (where x is any variable): b(x) The result of this command in a process description is to instantiate the variable x with the value received. In contrast, the action corresponding to passing a value on channel b is written as follows (where e is any valid expression): ’b(e) Thus, by using a co-name (i.e., something preceded by the CWB ’), we indicate an output/passing action. For example, the agent Negate continually receives a bit value on channel a and spits out its negation on channel a: const Bit = {0,1}