Plural_Forms::parse( string $str )

99		protected function parse( $str ) {100			$pos = 0;101			$len = strlen( $str );102 103			// Convert infix operators to postfix using the shunting-yard algorithm.104			$output = array();105			$stack  = array();106			while ( $pos < $len ) {107				$next = substr( $str, $pos, 1 );108 109				switch ( $next ) {110					// Ignore whitespace.111					case ' ':112					case "\t":113						++$pos;114						break;115 116					// Variable (n).117					case 'n':118						$output[] = array( 'var' );119						++$pos;120						break;121 122					// Parentheses.123					case '(':124						$stack[] = $next;125						++$pos;126						break;127 128					case ')':129						$found = false;130						while ( ! empty( $stack ) ) {131							$o2 = $stack[ count( $stack ) - 1 ];132							if ( '(' !== $o2 ) {133								$output[] = array( 'op', array_pop( $stack ) );134								continue;135							}136 137							// Discard open paren.138							array_pop( $stack );139							$found = true;140							break;141						}142 143						if ( ! $found ) {144							throw new Exception( 'Mismatched parentheses' );145						}146 147						++$pos;148						break;149 150					// Operators.151					case '|':152					case '&':153					case '>':154					case '<':155					case '!':156					case '=':157					case '%':158					case '?':159						$end_operator = strspn( $str, self::OP_CHARS, $pos );160						$operator     = substr( $str, $pos, $end_operator );161						if ( ! array_key_exists( $operator, self::$op_precedence ) ) {162							throw new Exception( sprintf( 'Unknown operator "%s"', $operator ) );163						}164 165						while ( ! empty( $stack ) ) {166							$o2 = $stack[ count( $stack ) - 1 ];167 168							// Ternary is right-associative in C.169							if ( '?:' === $operator || '?' === $operator ) {170								if ( self::$op_precedence[ $operator ] >= self::$op_precedence[ $o2 ] ) {171									break;172								}173							} elseif ( self::$op_precedence[ $operator ] > self::$op_precedence[ $o2 ] ) {174								break;175							}176 177							$output[] = array( 'op', array_pop( $stack ) );178						}