evaluateArithmetic function

String? evaluateArithmetic(String expr, Map<String, String> values, Map<String, String> types)

Evaluates a BODMAS arithmetic expression with variable substitution.

Identifiers in expr resolve from values; only variables whose types entry equals "number" may be used as operands. The grammar is + - * / with chained unary minus and no parentheses (matching the dashboard). Returns null on any error — unknown or non-numeric variable, division by zero, or malformed syntax.

Implementation

String? evaluateArithmetic(
  String expr,
  Map<String, String> values,
  Map<String, String> types,
) {
  // Resolve eagerly: every operand becomes a `double`, every operator a
  // single-char `String`. `null` means a bad character or an unusable variable.
  final tokens = _tokenize(expr, values, types);
  if (tokens == null) return null;

  try {
    final parser = _Parser(tokens);
    final result = parser.expression();
    if (!parser.atEnd) return null; // leftover tokens, e.g. "3 4"
    return _formatResult(result);
  } on _EvalError {
    return null;
  }
}