private static FOLLOW FindFollow(FOLLOWCollection followCollection, TreeNodeType target)
{
foreach (var item in followCollection)
{
if (item.Target == target)
{
return(item);
}
}
return(null);
}
public static void GetFollowCollection(
this RegulationList grammar,
out FOLLOWCollection followCollection,
Dictionary <TreeNodeType, bool> nullableDict = null,
FIRSTCollection firstCollection = null)
{
if (nullableDict == null)
{
grammar.GetNullableDict(out nullableDict);
}
if (firstCollection == null)
{
grammar.GetFirstCollection(out firstCollection, nullableDict);
}
FIRSTCollection firstList4Node;
grammar.GetFirstCollection4Node(out firstList4Node, nullableDict);
FIRSTCollection firstList4Regulation;
grammar.GetFirstCollection4Regulation(out firstList4Regulation, nullableDict, firstList4Node);
grammar.DoGetFollowList(out followCollection, nullableDict, firstList4Node);
}
public FirstListAndFollowList(FIRSTCollection firstList, FOLLOWCollection followList)
{
this.FirstList = firstList;
this.FollowList = followList;
}
/// <summary>
/// 计算文法的FOLLOW集
/// </summary>
/// <param name="grammar"></param>
/// <param name="nullableDict"></param>
/// <param name="firstList4Node"></param>
/// <returns></returns>
private static void DoGetFollowList(
this RegulationList grammar,
out FOLLOWCollection followCollection,
Dictionary <TreeNodeType, bool> nullableDict, FIRSTCollection firstList4Node)
{
// 初始化Follow list
followCollection = new FOLLOWCollection();
foreach (var item in grammar.GetAllTreeNodeNonLeaveTypes())
{
followCollection.TryInsert(new FOLLOW(item));
}
// 迭代到不动点
bool changed = false;
do
{
changed = false;
foreach (var regulation in grammar)
{
int count = regulation.RightPart.Count();
for (int index = 0; index < count; index++)
{
// 准备为target添加follow元素
TreeNodeType target = regulation.RightNode(index);
if (target.IsLeave)
{
continue;
} // 叶结点没有follow
FOLLOW follow = FindFollow(followCollection, target); // 找到follow对象
for (int checkCount = 0; checkCount < count - (index + 1); checkCount++)
{
if (Nullable(regulation.RightPart, index + 1, checkCount, nullableDict))
{
// nullable之后的FIRST是target的follow的一部分
FIRST first = FindFirst(
firstList4Node, regulation.RightNode(index + 1 + checkCount));
foreach (var value in first.Values)
{
if (value != TreeNodeType.NullNode)
{
changed = follow.TryInsert(value) || changed;
}
}
}
}
{
// 如果target之后的全部结点都是nullable，说明此regulation.Left的folow也是target的一部分。
if (Nullable(regulation.RightPart, index + 1, count - (index + 1), nullableDict))
{
// 找到此regulation.Left的folow
FOLLOW refFollow = FindFollow(followCollection, regulation.Left);
if (refFollow != follow)
{
foreach (var item in refFollow.Values)
{
changed = follow.TryInsert(item) || changed;
}
}
}
}
}
}
} while (changed);
}
