function units_mathematical_expression_create_from_infix in Units of Measurement 7.2

Create mathematical expression object from infix notation.

Parameters

string $infix_mathematical_expression: Mathematical expression written down in infix notation

Return value

\UnitsMathematicalExpressionWrapper In-memory representation of the provided mathematical expression

Throws

\UnitsMathematicalExpressionMalformedException

1 call to units_mathematical_expression_create_from_infix()

units_mathematical_expression_element_validate in ./units.module

Validate function for 'units_mathematical_expression' form element.

File

./units.module, line 683

Provide API for managing and converting units of measurement.

Code

function units_mathematical_expression_create_from_infix($infix_mathematical_expression) {
  $infix_mathematical_expression = array_filter(explode(' ', $infix_mathematical_expression), 'units_mathematical_expression_array_filter');
  if (empty($infix_mathematical_expression)) {
    return NULL;
  }
  $operators = units_get_operator_by_sign();

  // This is an implementation of shunting-yard algorithm.
  $stack = array();
  $output = array();
  foreach ($infix_mathematical_expression as $token) {
    if (is_numeric($token) || $token == UNITS_QUANTITY) {
      $output[] = $token;
    }
    elseif ($unit = units_unit_machine_name_load($token)) {
      $output[] = $unit
        ->toPostfix();
    }
    elseif (isset($operators[$token])) {
      while (!empty($stack) && isset($operators[$stack[count($stack) - 1]]) && $operators[$token]['precedence'] <= $operators[$stack[count($stack) - 1]]['precedence']) {
        $output[] = array_pop($stack);
      }
      $stack[] = $token;
    }
    elseif ($token == '(') {
      $stack[] = $token;
    }
    elseif ($token == ')') {
      while (!empty($stack) && end($stack) != '(') {
        $output[] = array_pop($stack);
      }

      // Popping out the opening parenthesis "(" symbol.
      array_pop($stack);
    }
    else {
      throw new UnitsMathematicalExpressionMalformedException(t('Unknown token: @token', array(
        '@token' => $token,
      )));
    }
  }
  while (!empty($stack)) {
    $output[] = array_pop($stack);
  }
  return units_mathematical_expression_create_from_postfix(implode(' ', $output));
}