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/*
* richard-atp-engine: A saturation-based automated theorem prover for first-order logic.
* Copyright (C) 2026 Richard Qin
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
#pragma once
/// @file term_bank.h
/// @brief Hash-consing term pool — guarantees structural sharing.
#include "atp/core/symbol_table.h"
#include "atp/core/term.h"
#include "atp/core/types.h"
#include <span>
#include <unordered_map>
#include <vector>
namespace atp {
/// Global term pool with hash-consing.
/// Every structurally identical term maps to the same TermId.
///
/// Holds a reference to SymbolTable for variable detection.
class TermBank {
public:
/// TermBank needs the SymbolTable to distinguish variables from constants
/// (both have 0 args, but SymbolKind differs).
explicit TermBank(SymbolTable& symbols) : symbols_(&symbols) {}
/// Create or retrieve a term. Returns the canonical TermId.
TermId makeTerm(SymbolId symbol, std::span<const TermId> args);
/// Create a variable term. Convenience for makeTerm(var, {}).
TermId makeVar(SymbolId var_symbol);
/// Look up a term by its ID.
[[nodiscard]] const Term& getTerm(TermId id) const;
/// Check if a TermId represents a variable (delegates to SymbolTable).
[[nodiscard]] bool isVariable(TermId id) const;
/// Total number of unique terms stored.
[[nodiscard]] size_t size() const;
/// Access the underlying SymbolTable.
[[nodiscard]] const SymbolTable& symbols() const { return *symbols_; }
[[nodiscard]] SymbolTable& mutableSymbols() { return *symbols_; }
private:
struct TermKey {
SymbolId symbol_;
std::vector<TermId> args_;
bool operator==(const TermKey& other) const = default;
};
struct TermKeyHash {
size_t operator()(const TermKey& key) const {
size_t seed = std::hash<uint32_t>{}(key.symbol_);
for (const TermId arg : key.args_) {
seed ^= std::hash<TermId>{}(arg) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
}
return seed;
}
};
SymbolTable* symbols_;
std::vector<Term> terms_;
std::unordered_map<TermKey, TermId, TermKeyHash> term_to_id_;
};
} // namespace atp
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