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/* Copyright (c) 2012-2017 The ANTLR Project. All rights reserved.
* Use of this file is governed by the BSD 3-clause license that
* can be found in the LICENSE.txt file in the project root.
*/
#pragma once
#include "antlr4-common.h"
namespace antlr4 {
namespace dfa {
/// <summary>
/// A DFA state represents a set of possible ATN configurations.
/// As Aho, Sethi, Ullman p. 117 says "The DFA uses its state
/// to keep track of all possible states the ATN can be in after
/// reading each input symbol. That is to say, after reading
/// input a1a2..an, the DFA is in a state that represents the
/// subset T of the states of the ATN that are reachable from the
/// ATN's start state along some path labeled a1a2..an."
/// In conventional NFA->DFA conversion, therefore, the subset T
/// would be a bitset representing the set of states the
/// ATN could be in. We need to track the alt predicted by each
/// state as well, however. More importantly, we need to maintain
/// a stack of states, tracking the closure operations as they
/// jump from rule to rule, emulating rule invocations (method calls).
/// I have to add a stack to simulate the proper lookahead sequences for
/// the underlying LL grammar from which the ATN was derived.
/// <p/>
/// I use a set of ATNConfig objects not simple states. An ATNConfig
/// is both a state (ala normal conversion) and a RuleContext describing
/// the chain of rules (if any) followed to arrive at that state.
/// <p/>
/// A DFA state may have multiple references to a particular state,
/// but with different ATN contexts (with same or different alts)
/// meaning that state was reached via a different set of rule invocations.
/// </summary>
class ANTLR4CPP_PUBLIC DFAState {
public:
class PredPrediction {
public:
Ref<atn::SemanticContext>
pred; // never null; at least SemanticContext.NONE
int alt;
PredPrediction(const Ref<atn::SemanticContext>& pred, int alt);
virtual ~PredPrediction();
virtual std::string toString();
private:
void InitializeInstanceFields();
};
int stateNumber;
std::unique_ptr<atn::ATNConfigSet> configs;
/// {@code edges[symbol]} points to target of symbol. Shift up by 1 so (-1)
/// <seealso cref="Token#EOF"/> maps to {@code edges[0]}.
// ml: this is a sparse list, so we use a map instead of a vector.
// Watch out: we no longer have the -1 offset, as it isn't needed anymore.
std::unordered_map<size_t, DFAState*> edges;
bool isAcceptState;
/// if accept state, what ttype do we match or alt do we predict?
/// This is set to <seealso cref="ATN#INVALID_ALT_NUMBER"/> when <seealso
/// cref="#predicates"/>{@code !=null} or <seealso
/// cref="#requiresFullContext"/>.
size_t prediction;
Ref<atn::LexerActionExecutor> lexerActionExecutor;
/// <summary>
/// Indicates that this state was created during SLL prediction that
/// discovered a conflict between the configurations in the state. Future
/// <seealso cref="ParserATNSimulator#execATN"/> invocations immediately
/// jumped doing full context prediction if this field is true.
/// </summary>
bool requiresFullContext;
/// <summary>
/// During SLL parsing, this is a list of predicates associated with the
/// ATN configurations of the DFA state. When we have predicates,
/// <seealso cref="#requiresFullContext"/> is {@code false} since full
/// context prediction evaluates predicates on-the-fly. If this is not null,
/// then <seealso cref="#prediction"/> is <seealso
/// cref="ATN#INVALID_ALT_NUMBER"/>.
/// <p/>
/// We only use these for non-<seealso cref="#requiresFullContext"/> but
/// conflicting states. That means we know from the context (it's $ or we
/// don't dip into outer context) that it's an ambiguity not a conflict.
/// <p/>
/// This list is computed by <seealso
/// cref="ParserATNSimulator#predicateDFAState"/>.
/// </summary>
std::vector<PredPrediction*> predicates;
/// Map a predicate to a predicted alternative.
DFAState();
DFAState(int state);
DFAState(std::unique_ptr<atn::ATNConfigSet> configs);
virtual ~DFAState();
/// <summary>
/// Get the set of all alts mentioned by all ATN configurations in this
/// DFA state.
/// </summary>
virtual std::set<size_t> getAltSet();
virtual size_t hashCode() const;
/// Two DFAState instances are equal if their ATN configuration sets
/// are the same. This method is used to see if a state already exists.
///
/// Because the number of alternatives and number of ATN configurations are
/// finite, there is a finite number of DFA states that can be processed.
/// This is necessary to show that the algorithm terminates.
///
/// Cannot test the DFA state numbers here because in
/// ParserATNSimulator#addDFAState we need to know if any other state
/// exists that has this exact set of ATN configurations. The
/// stateNumber is irrelevant.
bool operator==(const DFAState& o) const;
virtual std::string toString();
struct Hasher {
size_t operator()(DFAState* k) const { return k->hashCode(); }
};
struct Comparer {
bool operator()(DFAState* lhs, DFAState* rhs) const { return *lhs == *rhs; }
};
private:
void InitializeInstanceFields();
};
} // namespace dfa
} // namespace antlr4
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