public bool Alternative(Func <Ast> action)
{
using (ISnapshot snapshot = TakeSnapshot())
{
bool found = false;
try
{
int currIndex = Index;
Ast ast = action();
if (ast != null)
{
found = true;
_cachedAst[currIndex] = new Memo(ast, Index);
}
}
catch { }
snapshot.Rollback();
return(found);
}
}