calculator

Calculator DApp

Calculator is a DApp written in Python that evaluates mathematical expressions with the help of the Python Mathematical Expression Evaluator (py-expression-eval).

The DApp receives mathematical expressions as inputs and generates notices with the result of the corresponding evaluations. For example, the following expression is a valid input:

$$3 + 2 + 5 - 9$$

Interacting with the application

We can use the frontend-console application to interact with the DApp. Ensure that the application has already been built before using it.

First, go to a separate terminal window and switch to the frontend-console directory:

cd frontend-console

Then, send an input as follows:

yarn start input send --payload "3 + 2 + 5 - 9"

In order to verify the notices generated by your inputs, run the command:

yarn start notice list

The payload of the notice should be "1".

Running the environment in host mode

When developing an application, it is often important to easily test and debug it. For that matter, it is possible to run the Cartesi Rollups environment in host mode, so that the DApp's back-end can be executed directly on the host machine, allowing it to be debugged using regular development tools such as an IDE.

This DApp's back-end is written in Python, so to run it in your machine you need to have python3 installed.

In order to start the calculator back-end, run the following commands in a dedicated terminal:

cd calculator/
python3 -m venv .env
. .env/bin/activate
pip install -r requirements.txt
ROLLUP_HTTP_SERVER_URL="http://127.0.0.1:5004" python3 calculator.py

This will run the calculator back-end and send the corresponding notices to port 5004. It can optionally be configured in an IDE to allow interactive debugging using features like breakpoints.

You can also use a tool like entr to restart the back-end automatically when the code changes. For example:

ls *.py | ROLLUP_HTTP_SERVER_URL="http://127.0.0.1:5004" entr -r python3 calculator.py

After the back-end successfully starts, it should print an output like the following:

INFO:__main__:HTTP rollup_server url is http://127.0.0.1:5004
INFO:__main__:Sending finish

After that, you can interact with the application normally as explained above.