Visualizing ASTs

Abstract Syntax Trees (ASTs) are a way of representing the structure of code. They are useful in understanding how code works, especially when you need to analyse, transform or manipulate it.

To visualise the AST for a given code, we can use the Graphviz library. Graphviz is an open-source graph visualization software that allows you to visualise data structures like trees and graphs.

Installing Graphviz

Before we can visualise the AST using Graphviz, we need to install it on our system. The steps to install Graphviz on your system are as follows:

Windows

Download Graphviz from http://www.graphviz.org/download/
Add the following to your PATH environment variable:

C:\Program Files\Graphviz\bin
C:\Program Files\Graphviz\bin\dot.exe

Close any opened Jupyter notebook and the command prompt.

Linux

Run the following commands:

sudo apt-get update
sudo apt-get install graphviz

Alternatively, you can build it manually from http://www.graphviz.org/download/.

Installing the Graphviz module for Python

Once Graphviz is installed on your system, you need to install the Graphviz module for Python. You can install the module using pip or conda:

pip install graphviz

conda install graphviz

Visualising the AST

Now that we have installed Graphviz and the Graphviz module for Python, we can use it to visualise the AST for a Gossip code. Let’s take the following Gossip code as an example:

if 1 < 4 then{
print(4);
} else {
print(1);
};

To visualise the AST for this code, we need to first generate the AST using the main.py file provided in the Gossip repository. We can do this by running the following command:

python main.py -i -v

This will open the Gossip interpreter. We can then copy and paste the code into the interpreter and press enter. This will generate the AST for the code and display it.

Or it will also be saved as AST.png in the current directory. Below is the AST for the above code:

Explanantion

The visualizer.py file in the gossip/utils directory contains the code for visualizing the AST.

This code defines a class ASTViz that visualizes an abstract syntax tree (AST) using the graphviz library. The treebuilder method recursively traverses the AST and creates nodes and edges in the graphviz representation according to the type of each node in the AST. For example, if the node is an If statement, a diamond-shaped node is created in the graphviz representation with edges to the condition expression and the two possible execution paths. If the node is a While loop, an inverted triangle-shaped node is created with edges to the loop condition expression and the loop body. If the node is a BinOp, a node with the operator symbol is created with edges to the left and right operands.

The depth parameter is used to generate unique IDs for each node in the graphviz representation, and the code parameter is used as the label for the graph. When the treebuilder method is called with a depth of 0, the graphviz representation is rendered as a PNG image and displayed using the default viewer.