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Interpreter

Overview

The Interpreter in CodeSage is a Tree-Walk Interpreter that executes programs directly from the Abstract Syntax Tree (AST).
It recursively visits each AST node to evaluate expressions, execute statements, and manage variable scopes and environments.

It supports: - Control flow: if, elif, else, while, for, break, continue
- Functions: user-defined - Lists, indexing, and built-in operations (len, range)
- Runtime error handling

Responsibilities

  • Evaluate expressions (arithmetic, logical, comparison, unary, binary).
  • Execute statements (variable declarations, print, blocks, conditionals, loops, function definitions).
  • Manage environments and variable scopes.
  • Handle runtime errors (undefined variables, division by zero, invalid operations).
  • Provide runtime output for the IDE console.

Key Components

1.Environment

  • Stores variables and their values.
  • Supports nested scopes via enclosing environments.
  • Provides:
    • define(name, value) → creates a new variable
    • get(name_token) → retrieves a variable
    • assign(name_token, value) → updates a variable
    • get_at / assign_at → for resolved variable depths

2.Control Flow

Supports: - If / Elif / Else Statements - While Loops (with safety check for infinite loops) - For Loops (iterables and numeric ranges) - Break / Continue statements using exceptions

3.Functions

  • User-defined functions (PyFunction) support parameters, closures, and return values.
  • Native functions (e.g., clock) provide built-in utilities.
  • Function calls:
    • Verify the number of arguments matches the function’s arity.
    • Create a new environment for local variables.
    • Execute the function body.
    • Handle return values using ReturnException.

4.Expression Evaluation

  • Supports:

    • Literal, Unary, Binary, Grouping expressions
    • Variable lookup and assignment
    • Logical operators (and, or)
    • Function calls (call_expr)
    • Lists, indexing, and range expressions
    • Built-in operations: len(), range()

Example

x = 0
while (x < 3):
    print(x)
    x = x + 1
alt text

5.Runtime Error Handling

  • Error Type
  • Undefined Variable
  • Division by Zero
  • Invalid Operation
  • Index Out of Range
  • Non-iterable in For Loop

Errors are reported via CODESAGE.runtime_error with line number if available.

Example

x=5
print(x/0)
alt text

list=[1,2,3,4]
list[5]=6
alt text