Fix issue #21: Improve syntax validation and error messages

[jaybutani1793]

Fix issue #21: Improve syntax validation and error reporting

Problem

The current syntax validation provides generic error messages and does not clearly indicate the exact issue in malformed expressions. In some cases, incomplete expressions like "P v" or invalid symbols are not handled clearly.

Solution

• Added pre-validation step to detect incomplete expressions (e.g., dangling connectives like "P v")
• Added detection for invalid or unsupported symbols (e.g., "$", "%", "@", "#")
• Improved error messages to be more descriptive and user-friendly
• Included line number in error messages for better debugging

Implementation Details

• Introduced check_raw_connective_usage() to detect common typing mistakes before parsing
• Updated sen_data_evaluate() to:
  • Perform pre-validation on raw input
  • Return specific error messages with line numbers
  • Handle different syntax error types more clearly

Result

• Clear and precise error messages
• Better user feedback during proof construction
• Prevents misleading or vague syntax errors

Testing

Tested manually with the following cases:

1. Input: P v
   → Error: "Line X: Syntax error: connective missing operand"

2. Input: P $
   → Error: "Line X: Syntax error: invalid symbol or malformed expression"

3. Input: P v Q
   → Valid (no error)

4. Input: (P v Q
   → Error: mismatched parentheses

[jaybutani1793]

Thanks! I added more detailed syntax error messages, improved handling using switch cases, and ensured proper memory cleanup. This should improve clarity and user feedback.