public static ProductionRules GetFollow(ProductionRules rules)
{
ProductionRules first = GetFirst(rules);
List <string> nonTerminals = GetNonterminals(rules);
ProductionRules follow = new ProductionRules();
List <string> value = new List <string>();
for (int n = 0; n < nonTerminals.Count; ++n)
{
if (nonTerminals[n] == "S")
{
follow.Add(nonTerminals[n], "$");
}
for (int item = 0; item < rules.Count; ++item)
{
value.AddRange(rules[item].Value.Select(d => d.ToString()));
if (value.Contains(nonTerminals[n]))
{
for (int i = value.IndexOf(nonTerminals[n]); i < value.Count; i++)
{
try
{
if (Helper.IsLower(value[i + 1]))
{
follow.Add(nonTerminals[n], value[i + 1]);
break;
}
if (Helper.IsUpper(value[i + 1]))
{
for (int f = 0; f < first.Count; ++f)
{
if (first[f].Key == value[i + 1] && first[f].Value != "*")
{
follow.Add(nonTerminals[n], value[i + 1]);
}
}
}
}
catch (ArgumentOutOfRangeException)
{
var length = follow.Count;
for (int f = 0; f < length; ++f)
{
if (follow[f].Key == rules[item].Key && value[i] != rules[item].Key)
{
follow.Add(nonTerminals[n], follow[f].Value);
}
}
}
}
}
value.Clear();
}
}
return(follow);
}
static void Main(string[] args)
{
StreamReader reader = File.OpenText(@"C:\Users\Marinela\source\repos\LFPC LAB\LLParsing\rules.txt");
string line;
var productions = new ProductionRules();
while ((line = reader.ReadLine()) != null)
{
string[] rule = line.Split("->");
productions.Add(rule[0], rule[1]);
}
Console.WriteLine("Initial form of the grammar:");
Helper.Display(productions);
Console.WriteLine("Eliminate left recursion:");
productions.RemoveLeftRecursion(productions);
Helper.Display(productions);
Console.WriteLine("Obtain FIRST:");
List <KeyValuePair <string, string> > first = Parser.GetFirst(productions);
Helper.Display(first);
Console.WriteLine("Obtain FOLLOW:");
List <KeyValuePair <string, string> > follow = Parser.GetFollow(productions);
Helper.Display(follow);
}
public void ReadFromFile(string filename)
{
string[] lines = System.IO.File.ReadAllLines("../../Input/" + filename);
Nonterminals = new HashSet <string>(lines[0].Split(' '));
Terminals = new HashSet <string>(lines[1].Split(' '));
StartSymbol = lines[2];
foreach (var line in lines.Skip(3))
{
string[] elements = line.Split('?');
string[] right = elements[1].Split(' ');
var produRule = new ProductionRule()
{
Left = elements[0], Right = right.ToList()
};
ProductionRules.Add(produRule, count++);
}
Console.WriteLine("Terminals:");
foreach (var t in Terminals)
{
Console.Write(t + " ");
}
Console.WriteLine("\nNonterminals");
foreach (var t in Nonterminals)
{
Console.Write(t + " ");
}
Console.WriteLine("\nProduction rules");
foreach (var rule in ProductionRules)
{
Console.Write(rule.Key.Left + " -> " + String.Join(" ", rule.Key.Right) + " (" + rule.Value + ")");
Console.WriteLine();
}
}
public static ProductionRules GetFirst(ProductionRules rules)
{
ProductionRules first = new ProductionRules();
List <string> value = new List <string>();
for (int item = 0; item < rules.Count; ++item)
{
value.AddRange(rules[item].Value.Select(d => d.ToString()));
if (Helper.IsLower(value[0]))
{
first.Add(rules[item].Key, value[0]);
}
value.Clear();
}
do
{
for (int item = 0; item < rules.Count; ++item)
{
value.AddRange(rules[item].Value.Select(d => d.ToString()));
if (Helper.IsUpper(value[0]) && value[0] != "*")
{
for (int j = 0; j < first.Count; ++j)
{
if (first[j].Key.Contains(value[0]) && first[j].Value != "*")
{
first.Add(rules[item].Key, first[j].Value);
}
}
}
value.Clear();
}
}while (!AllCovered(rules, first));
while (rules.Count != first.Count)
{
Helper.GetDistinct(first);
}
Helper.GetDistinct(first);
return(first);
}