WC_Eval_Math::nfx() │ private static │ WC 1.0

Convert infix to postfix notation.

Method of the class: WC_Eval_Math{}

No Hooks.

Return

Array|String.

Usage

$result = WC_Eval_Math::nfx( $expr );

$expr(string) (required)

-

WC_Eval_Math::nfx() WC Eval Math::nfx code ^{WC 9.4.2}

private static function nfx( $expr ) {

	$index = 0;
	$stack = new WC_Eval_Math_Stack;
	$output = array(); // postfix form of expression, to be passed to pfx()
	$expr = trim( $expr );

	$ops   = array( '+', '-', '*', '/', '^', '_' );
	$ops_r = array( '+' => 0, '-' => 0, '*' => 0, '/' => 0, '^' => 1 ); // right-associative operator?
	$ops_p = array( '+' => 0, '-' => 0, '*' => 1, '/' => 1, '_' => 1, '^' => 2 ); // operator precedence

	$expecting_op = false; // we use this in syntax-checking the expression
	// and determining when a - is a negation
	if ( preg_match( "/[^\w\s+*^\/()\.,-]/", $expr, $matches ) ) { // make sure the characters are all good
		return self::trigger( "illegal character '{$matches[0]}'" );
	}

	while ( 1 ) { // 1 Infinite Loop ;)
		$op = substr( $expr, $index, 1 ); // get the first character at the current index
		// find out if we're currently at the beginning of a number/variable/function/parenthesis/operand
		$ex = preg_match( '/^([A-Za-z]\w*\(?|\d+(?:\.\d*)?|\.\d+|\()/', substr( $expr, $index ), $match );
		// ===============
		if ( '-' === $op and ! $expecting_op ) { // is it a negation instead of a minus?
			$stack->push( '_' ); // put a negation on the stack
			$index++;
		} elseif ( '_' === $op ) { // we have to explicitly deny this, because it's legal on the stack
			return self::trigger( "illegal character '_'" ); // but not in the input expression
			// ===============
		} elseif ( ( in_array( $op, $ops ) or $ex ) and $expecting_op ) { // are we putting an operator on the stack?
			if ( $ex ) { // are we expecting an operator but have a number/variable/function/opening parenthesis?
				$op = '*';
				$index--; // it's an implicit multiplication
			}
			// heart of the algorithm:
			while ( $stack->count > 0 and ( $o2 = $stack->last() ) and in_array( $o2, $ops ) and ( $ops_r[ $op ] ? $ops_p[ $op ] < $ops_p[ $o2 ] : $ops_p[ $op ] <= $ops_p[ $o2 ] ) ) {
				$output[] = $stack->pop(); // pop stuff off the stack into the output
			}
			// many thanks: https://en.wikipedia.org/wiki/Reverse_Polish_notation#The_algorithm_in_detail
			$stack->push( $op ); // finally put OUR operator onto the stack
			$index++;
			$expecting_op = false;
			// ===============
		} elseif ( ')' === $op && $expecting_op ) { // ready to close a parenthesis?
			while ( ( $o2 = $stack->pop() ) != '(' ) { // pop off the stack back to the last (
				if ( is_null( $o2 ) ) {
					return self::trigger( "unexpected ')'" );
				} else {
					$output[] = $o2;
				}
			}
			if ( preg_match( "/^([A-Za-z]\w*)\($/", $stack->last( 2 ), $matches ) ) { // did we just close a function?
				$fnn = $matches[1]; // get the function name
				$arg_count = $stack->pop(); // see how many arguments there were (cleverly stored on the stack, thank you)
				$output[] = $stack->pop(); // pop the function and push onto the output
				if ( in_array( $fnn, self::$fb ) ) { // check the argument count
					if ( $arg_count > 1 ) {
						return self::trigger( "too many arguments ($arg_count given, 1 expected)" );
					}
				} elseif ( array_key_exists( $fnn, self::$f ) ) {
					if ( count( self::$f[ $fnn ]['args'] ) != $arg_count ) {
						return self::trigger( "wrong number of arguments ($arg_count given, " . count( self::$f[ $fnn ]['args'] ) . " expected)" );
					}
				} else { // did we somehow push a non-function on the stack? this should never happen
					return self::trigger( "internal error" );
				}
			}
			$index++;
			// ===============
		} elseif ( ',' === $op and $expecting_op ) { // did we just finish a function argument?
			while ( ( $o2 = $stack->pop() ) != '(' ) {
				if ( is_null( $o2 ) ) {
					return self::trigger( "unexpected ','" ); // oops, never had a (
				} else {
					$output[] = $o2; // pop the argument expression stuff and push onto the output
				}
			}
			// make sure there was a function
			if ( ! preg_match( "/^([A-Za-z]\w*)\($/", $stack->last( 2 ), $matches ) ) {
				return self::trigger( "unexpected ','" );
			}
			$stack->push( $stack->pop() + 1 ); // increment the argument count
			$stack->push( '(' ); // put the ( back on, we'll need to pop back to it again
			$index++;
			$expecting_op = false;
			// ===============
		} elseif ( '(' === $op and ! $expecting_op ) {
			$stack->push( '(' ); // that was easy
			$index++;
			// ===============
		} elseif ( $ex and ! $expecting_op ) { // do we now have a function/variable/number?
			$expecting_op = true;
			$val = $match[1];
			if ( preg_match( "/^([A-Za-z]\w*)\($/", $val, $matches ) ) { // may be func, or variable w/ implicit multiplication against parentheses...
				if ( in_array( $matches[1], self::$fb ) or array_key_exists( $matches[1], self::$f ) ) { // it's a func
					$stack->push( $val );
					$stack->push( 1 );
					$stack->push( '(' );
					$expecting_op = false;
				} else { // it's a var w/ implicit multiplication
					$val = $matches[1];
					$output[] = $val;
				}
			} else { // it's a plain old var or num
				$output[] = $val;
			}
			$index += strlen( $val );
			// ===============
		} elseif ( ')' === $op ) { // miscellaneous error checking
			return self::trigger( "unexpected ')'" );
		} elseif ( in_array( $op, $ops ) and ! $expecting_op ) {
			return self::trigger( "unexpected operator '$op'" );
		} else { // I don't even want to know what you did to get here
			return self::trigger( "an unexpected error occurred" );
		}
		if ( strlen( $expr ) == $index ) {
			if ( in_array( $op, $ops ) ) { // did we end with an operator? bad.
				return self::trigger( "operator '$op' lacks operand" );
			} else {
				break;
			}
		}
		while ( substr( $expr, $index, 1 ) == ' ' ) { // step the index past whitespace (pretty much turns whitespace
			$index++;                             // into implicit multiplication if no operator is there)
		}
	}
	while ( ! is_null( $op = $stack->pop() ) ) { // pop everything off the stack and push onto output
		if ( '(' === $op ) {
			return self::trigger( "expecting ')'" ); // if there are (s on the stack, ()s were unbalanced
		}
		$output[] = $op;
	}
	return $output;
}