Step 6: Implement evaluator with TDD

- Eval(ast.Node) (float64, error) - recursive AST walker
- Handles all 4 operators: +, -, *, /
- Division by zero returns error
- Error propagation from sub-expressions
- 10 unit tests covering: single number, all operators, nested/deep
  expressions, division by zero (direct and in sub-expr), floats
2 files changed
tree: d15fcbe5f806449924e0ccb1c9953fec8ee9287f
  1. ast/
  2. cmd/
  3. docs/
  4. evaluator/
  5. lexer/
  6. parser/
  7. token/
  8. go.mod