6. Checklet Design

Extending the A$\lambda$goVista coop with a new checklet may seem like an involved process, but, fortunately, much has been automated. A typical upload involves the following steps:

1.

Produce an example query, for example $\ulcorner\hspace*{-2pt}$ (1,2)==>3 $\hspace*{-2pt}\urcorner$ for the IntAdd checklet.

2.

Submit the example query to A$\lambda$goVista's checklet template generator. Figure 11 shows the template produced from the query $\ulcorner\hspace*{-2pt}$ (1,2)==>3 $\hspace*{-2pt}\urcorner$.

3.

Fill in the Description() method with a short description of the problem the checklet tests for.

4.

Fill in the References() method with a list of hyper-references to on-line resources related to the problem.

5.

Replace ``return false'' in the Check() method with the relevant program checking code that returns true if the checklet accepts a query, and false otherwise. The Check() method takes an AlgoVista.CL.Object as argument, essentially the abstract syntax tree of a parsed query. The template already contains code to unpack this representation. For example, in Figure 11 intVal0 and intVal1 contain the input part of the query, and intVal2 the output part. Hence, in our example, ``return false'' would be replaced by ``return (intVal0+intVal1)==intVal2''

6.

Upload the new checklet to the A$\lambda$goVista server where it will be compiled, verified, and tested. A$\lambda$goVista will possibly return a list of compilation errors or security violations that have to be fixed before the checklet will be accepted into the coop.

 

The most difficult part is certainly constructing the actual program checking code. Inspiration can sometimes be had from the result checking literature [10,4,5,19,6,16,17], but more often by examining existing checklets. A$\lambda$goVista supports this by making the source code of checklets available for perusal.