Let’s Build An Interpreter In Python From Scratch

Part 5: Creating a Parser for Looping and Branching statement

This article is in continuation from: Part 4: Creating Parser for Variable Assignment and Printing

Till now we did the bare minimum for calculator with variable assignment. We have understood most of the basic concept in parsing let statement and printing statement. The last article should be enough to start parsing most of the statements. Addition of if and while statement is just for a quick revision to boost confidence.

While statement

The generic syntax of While Statement is:

while (condition) {
   statememt1;   # blocks
   statement2;
}

We can have list of statement inside the while. We call it block. it is quite common to see block of code in looping and branching statements or functions. We write a code for it first so we don’t have to rewrite it every time we define a new segment. Lets create a node with list of statement.

The eval for Block statement is same as interpreter. We go through each statement one by one and execute the code. Now lets create a parser for block statement. It is a…