public static Automaton CreateAutomaton(Grammar g)
{
//initialise to closure of start item
HashSet<ParseState> states = new HashSet<ParseState>();
states.Add(g.Productions.Where(a => a.Head.Equals(g.Root)).Select(a => new Item(a, 0)).Closure(g));
HashSet<ParseStateTransition> transitions = new HashSet<ParseStateTransition>();
HashSet<ParseState> sToAdd = new HashSet<ParseState>();
HashSet<ParseStateTransition> tToAdd = new HashSet<ParseStateTransition>();
do
{
sToAdd.Clear();
tToAdd.Clear();
foreach (var state in states)
{
foreach (var item in state)
{
if (item.Production.Body.Length == item.Position)
continue;
BnfTerm term = item.Production.Body[item.Position];
ParseState j = state.Goto(term, g);
sToAdd.Add(j);
tToAdd.Add(new ParseStateTransition(state, term, j));
}
}
}
while (states.UnionWithAddedCount(sToAdd) != 0 | transitions.UnionWithAddedCount(tToAdd) != 0);
return new Automaton(transitions, g);
}
public static ParseState Closure(this IEnumerable<Item> items, Grammar grammar)
{
HashSet<Item> closure = new HashSet<Item>(items);
HashSet<Item> toAdd = new HashSet<Item>();
do
{
toAdd.Clear();
foreach (var item in closure)
{
if (item.Position == item.Production.Body.Length)
continue;
BnfTerm term = item.Production.Body[item.Position];
if (term is NonTerminal)
{
NonTerminal nonTerm = term as NonTerminal;
foreach (var production in grammar.Productions.Where(a => a.Head.Equals(nonTerm)))
toAdd.Add(new Item(production, 0));
}
}
}
while (closure.UnionWithAddedCount(toAdd) > 0);
return new ParseState(closure, IsAcceptingState(closure, grammar));
}
public static Grammar ConstructTestGrammar(out NonTerminal S, out NonTerminal T, out NonTerminal F)
{
T = new NonTerminal("T");
F = new NonTerminal("F");
T.Rules = T + "*" + F | F;
F.Rules = "(" + T + ")" | new Terminal("ID", "([A-Z]|[a-z])+");
var g = new Grammar(T, new Terminal(" ", isIgnored:true));
S = g.Root;
return g;
}
public void GetFirstSetWithEmptyStrings()
{
NonTerminal a = new NonTerminal("A");
NonTerminal b = new NonTerminal("B");
a.Rules = b + "s";
b.Rules = "".AsTerminal() | "x";
Grammar g = new Grammar(a);
var set = g.GetFirstSet(a);
Assert.IsNotNull(set);
Assert.AreEqual(2, set.Count);
Assert.IsTrue(set.Contains("x"));
Assert.IsTrue(set.Contains("s"));
}
private IEnumerable<Item> CalculateInitialState(out Grammar g, out NonTerminal S, out NonTerminal T, out NonTerminal F)
{
S = new NonTerminal("S");
var sCopy = S;
T = new NonTerminal("T");
F = new NonTerminal("F");
S.Rules = T + "$";
T.Rules = T + "*" + F | F;
F.Rules = "(" + T + ")" | new Terminal("ID", "([A-Z]|[a-z])+");
g = new Grammar(S, new Terminal(" "));
Item start = new Item(g.Productions.First(a => a.Head.Equals(sCopy)), 0);
return new[] { start }.Closure(g);
}
public static ParseState Goto(this IEnumerable<Item> state, BnfTerm symbol, Grammar grammar)
{
HashSet<Item> items = new HashSet<Item>();
foreach (var item in state)
{
if (item.Production.Body.Length == item.Position)
continue;
BnfTerm term = item.Production.Body[item.Position];
if (term.Equals(symbol))
items.Add(new Item(item.Production, item.Position + 1));
}
return items.Closure(grammar);
}
public void GetFirstSet()
{
NonTerminal a = new NonTerminal("A");
NonTerminal b = new NonTerminal("B");
NonTerminal c = new NonTerminal("C");
NonTerminal d = new NonTerminal("D");
a.Rules = b + d | c + d;
b.Rules = "b";
c.Rules = "c";
d.Rules = "d";
Grammar g = new Grammar(a);
var set = g.GetFirstSet(a);
Assert.IsNotNull(set);
Assert.AreEqual(2, set.Count);
Assert.IsFalse(set.Contains("d"));
Assert.IsTrue(set.Contains("b"));
Assert.IsTrue(set.Contains("c"));
}
public void ConstructAGrammar()
{
NonTerminal op = new NonTerminal("Operator");
NonTerminal expr = new NonTerminal("Expression");
Terminal number = new Terminal("Number", @"\b\d+\b");
Terminal plus = new Terminal("Plus", @"\+");
Terminal multiply = @"\*";
op.Rules = plus | multiply;
expr.Rules = number + op + expr;
Terminal whitespace = new Terminal("Whitespace", " |\n|\r", true);
Grammar g = new Grammar(expr, whitespace);
Assert.AreEqual(3, g.Terminals.Count());
Assert.AreEqual(3, g.NonTerminals.Count()); //Although the grammar only specifies 2 Nonterminals, grammar creates 1 internally for the root
Lexer lexer = g.CreateLexer("1 + 2 * 3");
Assert.AreEqual(5, lexer.Count());
}
public Automaton(IEnumerable<ParseStateTransition> transitions, Grammar grammar)
{
this.grammar = grammar;
foreach (var transition in transitions)
{
allStates.Add(transition.Start);
allStates.Add(transition.End);
Dictionary<BnfTerm, ParseState> d;
if (!transitionRules.TryGetValue(transition.Start, out d))
{
d = new Dictionary<BnfTerm, ParseState>();
transitionRules.Add(transition.Start, d);
}
if (d.ContainsKey(transition.Trigger))
throw new InvalidOperationException("Duplicate transition");
d[transition.Trigger] = transition.End;
}
}
public void GetFollowSet()
{
NonTerminal a = new NonTerminal("A");
NonTerminal b = new NonTerminal("B");
a.Rules = "a" + b;
b.Rules = b + "a" | "c";
Grammar g = new Grammar(a);
var followA = g.GetFollowSet(a);
Assert.AreEqual(0, followA.Count);
var followB = g.GetFollowSet(b);
Assert.AreEqual(1, followB.Count);
Assert.IsTrue(followB.Contains("a"));
}
public void IsNullable()
{
NonTerminal a = new NonTerminal("A");
NonTerminal b = new NonTerminal("B");
NonTerminal c = new NonTerminal("C");
a.Rules = b + "s";
b.Rules = "".AsTerminal() | c;
c.Rules = "c";
Grammar g = new Grammar(a);
Assert.IsTrue(b.IsNullable);
Assert.IsFalse(a.IsNullable);
Assert.IsFalse(c.IsNullable);
}
public RecursiveDescentParser(Grammar g)
: base(g)
{
ConstructPredictiveParseTable();
}
public Parser(Grammar grammar)
{
Grammar = grammar;
}
public static bool IsAcceptingState(this IEnumerable<Item> items, Grammar grammar)
{
return items
.Where(a => a.Production.Head.Equals(grammar.Root))
.Any(a => a.Position == a.Production.Body.Length);
}
public SLR1(Grammar grammar)
: base(grammar)
{
}
private ParseState MakeStateState(NonTerminal root, Grammar g)
{
return new HashSet<Item>(root.Rules.Select(a => new Item(new Production(root, a), 0))).Closure(g);
}
public LRParserBase(Grammar g)
: base(g)
{
}
public LR0(Grammar grammar)
: base(grammar)
{
automaton = CreateAutomaton(grammar);
}