errors.py

def string_with_arrows(text, pos_start, pos_end):
	result = ''

	# Calculate indices
	idx_start = max(text.rfind('\n', 0, pos_start.idx), 0)
	idx_end = text.find('\n', idx_start + 1)
	if idx_end < 0: idx_end = len(text)
	
	# Generate each line
	line_count = pos_end.ln - pos_start.ln + 1
	for i in range(line_count):
		# Calculate line columns
		line = text[idx_start:idx_end]
		col_start = pos_start.col if i == 0 else 0
		col_end = pos_end.col if i == line_count - 1 else len(line) - 1

		# Append to result
		result += line + '\n'
		result += ' ' * col_start + '^' * (col_end - col_start)

		# Re-calculate indices
		idx_start = idx_end
		idx_end = text.find('\n', idx_start + 1)
		if idx_end < 0: idx_end = len(text)

	return result.replace('\t', '')
  
class Error:
  def __init__(self, pos_start, pos_end, error_name, details):
    self.pos_start = pos_start
    self.pos_end = pos_end
    self.error_name = error_name
    self.details = details
  
  def as_string(self):
    result  = f'{self.error_name}: {self.details}\n'
    result += f'File {self.pos_start.fn}, line {self.pos_start.ln + 1}'
    result += '\n\n' + string_with_arrows(self.pos_start.ftxt, self.pos_start, self.pos_end)
    return result

class IllegalCharError(Error):
  def __init__(self, pos_start, pos_end, details):
    super().__init__(pos_start, pos_end, 'Illegal Character', details)

class ExpectedCharError(Error):
  def __init__(self, pos_start, pos_end, details):
    super().__init__(pos_start, pos_end, 'Expected Character', details)

class InvalidSyntaxError(Error):
  def __init__(self, pos_start, pos_end, details=''):
    super().__init__(pos_start, pos_end, 'Invalid Syntax', details)

class RTError(Error):
  def __init__(self, pos_start, pos_end, details, context):
    super().__init__(pos_start, pos_end, 'Runtime Error', details)
    self.context = context

  def as_string(self):
    result  = self.generate_traceback()
    result += f'{self.error_name}: {self.details}'
    result += '\n\n' + string_with_arrows(self.pos_start.ftxt, self.pos_start, self.pos_end)
    return result

  def generate_traceback(self):
    result = ''
    pos = self.pos_start
    ctx = self.context

    while ctx:
      result = f'  File {pos.fn}, line {str(pos.ln + 1)}, in {ctx.display_name}\n' + result
      pos = ctx.parent_entry_pos
      ctx = ctx.parent

    return 'Traceback (most recent call last):\n' + result