We have put together a byte (8 bits) of examples of SPARK code on a server in the cloud here. (many thanks Nico Setton for that!)

Each example consists in very few lines, a few files at most, and demoes an interesting feature of SPARK. The initial version is incorrect, and hitting the "Prove" button will return with messages that point to the errors. By following the suggested fix in comments you should be able to get the code to prove automatically.

Of course, you could already do this by installing yourself SPARK GPL on a machine (download here and follow these instructions to install additional provers). The benefit with this webpage is that anyone can now experiment live with SPARK without installing first the toolset. This is very much inspired from what Microsoft Research has done with other verification tools as part of their rise4fun website.

Something particularly interesting for academics is that all the code for this widget is open source. So you can setup your own proof server for hands-on sessions, with your own exercises, in a matter of minutes! Just clone the code_examples_server project from GitHub, follow the instructions in the README, populate your server with your exercises and examples, and you're set! No need to ask for IT to setup all boxes for your students, they just need a browser to point to your server location. An exercise consists in a directory with:

a file example.yaml with the name and description of the exercise (in YAML syntax)

a GNAT project file main.gpr (could be almost empty, or force the use of SPARK_Mode so that all the code is analyzed)

the source files for this exercise

For inspiration, see the examples from the Compile_And_Prove_Demo project from GitHub, inside directory 'examples', which were used to populate our little online proof webpage.

Feel free to report problems or suggest improvements to the widget or the examples on their respective GitHub project pages.