/// <summary>
/// Print First and Follow sets for all non-terminal symbols.
/// </summary>
public static void PrintFirstAndFollowSets <TTokenKind, TNonterminal>(
this Grammar <TTokenKind, TNonterminal> grammar,
TextWriter writer
)
where TTokenKind : struct, Enum
where TNonterminal : struct, Enum
{
var table = new TableBuilder()
.SetTitle("First and Follow sets")
.SetColumns(new Column("Variable", 12),
new Column("Nullable", 12),
new Column("First", 16),
new Column("Follow", 16))
.Build();
var tableWriter = new TextTableWriter(table, writer);
tableWriter.WriteHead();
foreach (Nonterminal variable in grammar.Nonterminals)
{
tableWriter.WriteRow(variable.Name,
grammar.Erasable(variable).FormatBoolean(),
grammar.First(variable).ToVectorString(),
grammar.Follow(variable).ToVectorString());
}
tableWriter.WriteFooter();
}
public static void PrintParsingTable <TTokenKind, TNonterminal>(
this IShiftReduceParser <TTokenKind, TNonterminal> parser,
TextWriter writer
)
where TTokenKind : struct, Enum
where TNonterminal : struct, Enum
{
var actionTable = new TableBuilder()
.SetTitle("ACTION")
.SetColumns(new Column("State", 8).AsSingletonEnumerable()
.Concat(parser.Terminals.Select(token => new Column(token.Name, 5))))
.Build();
var actionTableWriter = new TextTableWriter(actionTable, writer);
actionTableWriter.WriteHead();
foreach (var state in parser.GetStates())
{
actionTableWriter.WriteRow(state.ToString().AsSingletonEnumerable()
.Concat(parser.Terminals.Select(terminal => parser.Action(state, terminal).ToTableString())).ToArray());
}
actionTableWriter.WriteFooter();
var gotoTable = new TableBuilder()
.SetTitle("GOTO")
.SetColumns(new Column("State", 8).AsSingletonEnumerable()
.Concat(parser.TrimmedNonTerminalSymbols.Select(nonterminal => new Column(nonterminal.Name, 5))))
.Build();
var gotoTableWriter = new TextTableWriter(gotoTable, writer);
gotoTableWriter.WriteHead();
foreach (var state in parser.GetStates())
{
gotoTableWriter.WriteRow(state.ToString().AsSingletonEnumerable()
.Concat(parser.TrimmedNonTerminalSymbols.Select(nonterminal => parser.Goto(state, nonterminal).ToGotoTableString())).ToArray());
}
gotoTableWriter.WriteFooter();
}
// Driver program here
public static void Parse <TTokenKind>(
this IShiftReduceParsingTable <TTokenKind> parser,
ILexer <Token <TTokenKind> > lexer,
TextWriter logger = null
) where TTokenKind : struct, Enum
{
var table = new TableBuilder()
.SetColumns(new Column("SeqNo", 8),
new Column("Stack", 14, Align.Left),
new Column("Symbols", 14, Align.Left),
new Column("Input", 10, Align.Right),
new Column("Action", 34, Align.Left))
.Build();
int seqNo = 1;
int ip = 0;
TableWriter tableWriter = null;
if (logger != null)
{
tableWriter = new TextTableWriter(table, logger);
tableWriter.WriteHead();
}
// stack of states (each state uniquely identifies a symbol, such that each
// configuration (s(0)s(1)...s(m), a(i)a(i+1)...a(n)$) of the parser can generate a
// right sentential form X(1)X(2)...X(m)a(i+1)...a(n)$). That is X(i) is the grammar
// symbol associated with state s(i), i > 0. Note the s(0) is the only state not associated
// with a grammar symbol, because this state represents the initial state og the LR(0) automaton
// and its role is as a bottom-of-stack marker we can use to accept the parsed string.
var stack = new Stack <int>();
// push initial state onto the stack
stack.Push(parser.StartState);
Token <TTokenKind> token = lexer.GetNextToken();
Terminal <TTokenKind> a = parser.Terminals[token.Kind];
while (true)
{
int s = stack.Peek();
var action = parser.Action(s, a);
// Action(s, a) = shift t
if (action.IsShift) // consume input token here
{
// push t onto the stack
int t = action.ShiftToState;
if (lexer is IBufferedLexer <Token <TTokenKind> > fake)
{
// output 'shift t'
tableWriter?.WriteRow($"({seqNo++})",
$" {string.Join(" ", stack.Reverse())}",
$" {string.Join(" ", stack.Reverse().Skip(1).Select(state => parser.GetItems(state).SpellingSymbol.Name))}",
$"{fake.GetRemainingTokens(ip++).Aggregate(new StringBuilder(), (sb, tok) => sb.Append(tok.Text))} ",
$" shift {t}");
}
else
{
// output 'shift t'
tableWriter?.WriteRow($"({seqNo++})",
$" {string.Join(" ", stack.Reverse())}",
$" {string.Join(" ", stack.Reverse().Skip(1).Select(state => parser.GetItems(state).SpellingSymbol.Name))}",
" ",
$" shift {t}");
}
stack.Push(t);
// call yylex to get the next token
token = lexer.GetNextToken();
a = parser.Terminals[token.Kind];
}
// Action(s, a) = reduce A → β (DFA recognized a handle)
else if (action.IsReduce) // remaining input remains unchanged
{
Production p = parser.Productions[action.ReduceToProductionIndex];
// output 'reduce by A → β'
string[] values = null;
if (tableWriter != null)
{
if (lexer is IBufferedLexer <Token <TTokenKind> > fake)
{
values = new[]
{
$"({seqNo++})",
$" {string.Join(" ", stack.Reverse())}",
$" {string.Join(" ", stack.Reverse().Skip(1).Select(state => parser.GetItems(state).SpellingSymbol.Name))}",
$"{fake.GetRemainingTokens(ip).Aggregate(new StringBuilder(), (sb, tok) => sb.Append(tok.Text))} ",
$" reduce by {p}"
};
}
else
{
values = new[]
{
$"({seqNo++})",
$" {string.Join(" ", stack.Reverse())}",
$" {string.Join(" ", stack.Reverse().Skip(1).Select(state => parser.GetItems(state).SpellingSymbol.Name))}",
" ",
$" reduce by {p}"
};
}
}
// pop |β| symbols off the stack
stack.PopItemsOfLength(p.Length);
// let state t now be on top of the stack
int t = stack.Peek();
// push GOTO(t, A) onto the stack
int v = parser.Goto(t, p.Head);
stack.Push(v);
if (tableWriter != null)
{
values[4] += $", goto {v}";
tableWriter.WriteRow(values);
}
// TODO: Create a new AST node for the (semantic) rule A → β, and build AST
}
// DFA recognized a the accept handle of the initial item set
else if (action.IsAccept)
{
// TODO: Should this be validated here???
Debug.Assert(lexer.GetNextToken().IsEof);
if (lexer is IBufferedLexer <Token <TTokenKind> > fake)
{
// output accept
tableWriter?.WriteRow($"({seqNo})",
$" {string.Join(" ", stack.Reverse())}",
$" {string.Join(" ", stack.Reverse().Skip(1).Select(state => parser.GetItems(state).SpellingSymbol.Name))}",
$"{fake.GetRemainingTokens(ip).Aggregate(new StringBuilder(), (sb, tok) => sb.Append(tok.Text))} ",
$" {action}");
}
else
{
// output accept
tableWriter?.WriteRow($"({seqNo})",
$" {string.Join(" ", stack.Reverse())}",
$" {string.Join(" ", stack.Reverse().Skip(1).Select(state => parser.GetItems(state).SpellingSymbol.Name))}",
" ",
$" {action}");
}
break;
}
else
{
// error
throw new InvalidOperationException($"Unexpected symbol: {a.Name}");
}
}
tableWriter?.WriteFooter();
}