reimplement V8 unbounded regexp optimisation pattern

alib2algo/src/regexp/simplify/RegExpOptimizeUnboundedPart.hpp

@@ -766,16 +766,16 @@ bool RegExpOptimize::V6( UnboundedRegExpAlternation < SymbolType > & /* node */
   * @return bool true if optimization applied else false
   */
 template < class SymbolType >
-bool RegExpOptimize::V8( UnboundedRegExpConcatenation < SymbolType > & /* node */ ) {
+bool RegExpOptimize::V8( UnboundedRegExpConcatenation < SymbolType > & node ) {
 	bool optimized = false;
 	// interpretation: if there is iteration in concatenation node, and element of iteration contains eps and is straight before this iteration, then this element can be omitted
-	/*if ( node.getChildren ( ).size ( ) == 0 )
+	if ( node.getChildren ( ).size ( ) == 0 )
 		return false;
-	for( auto it = next ( node.getChildren ( ).begin( ) ); it != node.getChildren ( ).end( ); ) {
-		UnboundedRegExpIteration < SymbolType > * iter = dynamic_cast < UnboundedRegExpIteration < SymbolType > * > ( & * it );
+	for( auto it = node.getChildren ( ).begin( ); it != node.getChildren ( ).end( ); ) {
+		const UnboundedRegExpIteration < SymbolType > * iter = dynamic_cast < const UnboundedRegExpIteration < SymbolType > * > ( & * it );
 		if( ! iter ) {
 			++ it;
@@ -783,7 +783,7 @@ bool RegExpOptimize::V8( UnboundedRegExpConcatenation < SymbolType > & /* node *
 		}
 		// if element of iteration is concatenation, we need to check this specially
-		UnboundedRegExpConcatenation < SymbolType > * concat = dynamic_cast < UnboundedRegExpConcatenation < SymbolType > * > ( & iter->getChild ( ) );
+		const UnboundedRegExpConcatenation < SymbolType > * concat = dynamic_cast < const UnboundedRegExpConcatenation < SymbolType > * > ( & iter->getChild ( ) );
 		if( concat ) {
 			// check if not out of bounds
@@ -800,23 +800,25 @@ bool RegExpOptimize::V8( UnboundedRegExpConcatenation < SymbolType > & /* node *
 				equal ( concat->getChildren ( ).begin( ), concat->getChildren ( ).end( ), it2, [ ] ( const UnboundedRegExpElement < SymbolType > & a, const UnboundedRegExpElement < SymbolType > & b ) -> bool { return a == b; } ) ) {
 				optimized = true;
-				it = node.getChildren ( ).erase ( it2, it );
+				it = node.erase ( it2, it );
 			} else
 				++ it;
 		} else {
+			// check if not at the first node
+			if ( it == node.getChildren ( ).begin ( ) ) {
+				it ++;
+				continue;
+			}
+
 			auto prev = std::prev ( it );
 			if ( regexp::properties::RegExpEpsilon::languageContainsEpsilon ( iter->getElement ( ) ) && iter->getElement ( ) == * prev ) {
-				it = node.getChildren ( ).erase ( prev );
+				it = node.erase ( prev );
 				optimized = true;
-
-				// in case xxx*, we need to stay on the iter element, not to go behind it
-				if( it != node.getChildren().begin( ) )
-					it = std::prev( it );
 			} else
 				++ it;
 		}
-	}*/
+	}
 	return optimized;
 }