Devlog1

What is a symbol table?

Symbol table stores current program state. I separated it into three levels, turning SymbolTable into a kind of manager-facade:

1. FileTable. Contains classes, objects and functions in current file.
2. variableTable. Contains functions and properties of current instance (if ClassA.someClassFunction() is resolved, instance of ClassA is a variableTable in current SymbolTable). Variable table is not a special class, it’s either a primitive or a class instance.
3. ScopeTable. Contains all variables and arguments for current function.

Introduction

I created global SymbolTable globalTable and global imports. It was convenient at the time. All classes, functions and objects are added to the globalTable during semantic analysis. Superclasses are defined, imports too. Semantic analysis is performed for initial file and all its dependencies (they are files). It is handy to write imports and file contents to global variables. But when I started writing tests, it backfired.

Running tests

When running a program once, evaluation is done once. However, when running tests, evaluation runs many times. It lead to all kinds of issues:

1. Functions appeared twice, especially mains, because main in current file and main from previous failed session were saved.
2. Phantom functions were called from unclean imports

To fix that, I added clear() function to make global Table a blank table and delete all imports. It is called at the end of evaluate() and eval() (which is a light version of evaluate()). But it was treating a symptom, not dealing with a problem. I plan to make it possible to run multiple threads in parallel. So I need to remove these globals. Probably I can create an array of global tables, each thread will write to a separate table, although I would like to make stateless code, not add another crutch.

Then I discovered same problems with tests that check failure behavior. Particularly check whether exceptions are thrown correctly. It appeared they did, however a clean program state wasn’t restored after. Exception was thrown, but globalTable and imports weren’t cleared after. I added clear() on PositionalException initialization.

Future work

Add imports to FileTable as a property. Remove globalTable and pass it as an argument.

Main | Writings | Drawings