05 Interpreting

[ngjunsiang]

Let's start changing state by interpreting the code.

[ngjunsiang]

Executing statements

Let's execute statements as well, starting with the OUTPUT statement we implemented in the previous notebook.

For now, we only have OUTPUT statements to execute. When we have more kinds of statements, they too will go into the if-else cascade.

[102ed45]

[ngjunsiang]

Interpreting

Our interpreter runs the following in a loop:
https://github.com/nyjc-computing/pseudo/blob/9dc3aa28dbfd607def076b19591878d0392045bb/interpreter.py#L22-L28

It takes the list of statements from the parser, and execute()s them to bring about their effects.

We catch any errors that occur, and raise our own custom RuntimeError instead.

[ngjunsiang]

Main loop

The main program loop :

1. passes src to the scanner and gets tokens,
2. passes tokens to the parser and gets statements,
3. passes statements to the interpreter,
4. exits.

[acc19e7]

[ngjunsiang]

Exit codes

We also attempt to use proper system exit codes as documented in https://nixdoc.net/man-pages/FreeBSD/man3/sysexits.3.html, but this is not the focus for now.

https://github.com/nyjc-computing/pseudo/blob/acc19e752dafd7fead8a5a59b445e9f96c787a5d/main.py#L20

https://github.com/nyjc-computing/pseudo/blob/acc19e752dafd7fead8a5a59b445e9f96c787a5d/main.py#L25

[ngjunsiang]

Testing

if __name__ == "__main__":
    main()

Result:

Hello, everyone!

[39779f8]