path: root/libsolidity/formal/Why3Translator.cpp

/*
    This file is part of solidity.

    solidity 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.

    solidity 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 solidity.  If not, see <http://www.gnu.org/licenses/>.
*/
/**
 * @author Christian <c@ethdev.com>
 * @date 2015
 * Component that translates Solidity code into the why3 programming language.
 */

#include <libsolidity/formal/Why3Translator.h>
#include <boost/algorithm/string/predicate.hpp>

using namespace std;
using namespace dev;
using namespace dev::solidity;

bool Why3Translator::process(SourceUnit const& _source)
{
    try
    {
        if (m_lines.size() != 1 || !m_lines.back().contents.empty())
            fatalError(_source, "Multiple source units not yet supported");
        appendPreface();
        _source.accept(*this);
    }
    catch (NoFormalType&)
    {
        solAssert(false, "There is a call to toFormalType() that does not catch NoFormalType exceptions.");
    }
    catch (FatalError& /*_e*/)
    {
        solAssert(m_errorOccured, "");
    }
    return !m_errorOccured;
}

string Why3Translator::translation() const
{
    string result;
    for (auto const& line: m_lines)
        result += string(line.indentation, '\t') + line.contents + "\n";
    return result;
}

void Why3Translator::error(ASTNode const& _node, string const& _description)
{
    auto err = make_shared<Error>(Error::Type::Why3TranslatorError);
    *err <<
        errinfo_sourceLocation(_node.location()) <<
        errinfo_comment(_description);
    m_errors.push_back(err);
    m_errorOccured = true;
}

void Why3Translator::fatalError(ASTNode const& _node, string const& _description)
{
    error(_node, _description);
    BOOST_THROW_EXCEPTION(FatalError());
}

string Why3Translator::toFormalType(Type const& _type) const
{
    if (_type.category() == Type::Category::Bool)
        return "bool";
    else if (auto type = dynamic_cast<IntegerType const*>(&_type))
    {
        if (!type->isAddress() && !type->isSigned() && type->numBits() == 256)
            return "uint256";
    }
    else if (auto type = dynamic_cast<ArrayType const*>(&_type))
    {
        if (!type->isByteArray() && type->isDynamicallySized() && type->dataStoredIn(DataLocation::Memory))
        {
            // Not catching NoFormalType exception.  Let the caller deal with it.
            string base = toFormalType(*type->baseType());
            return "array " + base;
        }
    }
    else if (auto mappingType = dynamic_cast<MappingType const*>(&_type))
    {
        solAssert(mappingType->keyType(), "A mappingType misses a keyType.");
        if (dynamic_cast<IntegerType const*>(&*mappingType->keyType()))
        {
            //@TODO Use the information from the key type and specify the length of the array as an invariant.
            // Also the constructor need to specify the length of the array.
            solAssert(mappingType->valueType(), "A mappingType misses a valueType.");
            // Not catching NoFormalType exception.  Let the caller deal with it.
            string valueTypeFormal = toFormalType(*mappingType->valueType());
            return "array " + valueTypeFormal;
        }
    }

    BOOST_THROW_EXCEPTION(NoFormalType()
        << errinfo_noFormalTypeFrom(_type.toString(true)));
}

void Why3Translator::addLine(string const& _line)
{
    newLine();
    add(_line);
    newLine();
}

void Why3Translator::add(string const& _str)
{
    m_lines.back().contents += _str;
}

void Why3Translator::newLine()
{
    if (!m_lines.back().contents.empty())
        m_lines.push_back({"", m_lines.back().indentation});
}

void Why3Translator::unindent()
{
    newLine();
    solAssert(m_lines.back().indentation > 0, "");
    m_lines.back().indentation--;
}

bool Why3Translator::visit(ContractDefinition const& _contract)
{
    if (m_seenContract)
        error(_contract, "More than one contract not supported.");
    m_seenContract = true;
    m_currentContract.contract = &_contract;
    if (_contract.isLibrary())
        error(_contract, "Libraries not supported.");

    addLine("module Contract_" + _contract.name());
    indent();
    addLine("use import int.Int");
    addLine("use import ref.Ref");
    addLine("use import map.Map");
    addLine("use import array.Array");
    addLine("use import int.ComputerDivision");
    addLine("use import mach.int.Unsigned");
    addLine("use import UInt256");
    addLine("exception Revert");
    addLine("exception Return");

    if (_contract.stateVariables().empty())
        addLine("type state = ()");
    else
    {
        addLine("type state = {");
        indent();
        m_currentContract.stateVariables = _contract.stateVariables();
        for (VariableDeclaration const* variable: m_currentContract.stateVariables)
        {
            string varType;
            try
            {
                varType = toFormalType(*variable->annotation().type);
            }
            catch (NoFormalType &err)
            {
                string const* typeNamePtr = boost::get_error_info<errinfo_noFormalTypeFrom>(err);
                string typeName = typeNamePtr ? " \"" + *typeNamePtr + "\"" : "";
                fatalError(*variable, "Type" + typeName + " not supported for state variable.");
            }
            addLine("mutable _" + variable->name() + ": " + varType);
        }
        unindent();
        addLine("}");
    }

    addLine("type account = {");
    indent();
    addLine("mutable balance: uint256;");
    addLine("storage: state");
    unindent();
    addLine("}");

    addLine("val external_call (this: account): bool");
    indent();
    addLine("ensures { result = false -> this = (old this) }");
    addLine("writes { this }");
    addSourceFromDocStrings(m_currentContract.contract->annotation());
    unindent();

    if (!_contract.baseContracts().empty())
        error(*_contract.baseContracts().front(), "Inheritance not supported.");
    if (!_contract.definedStructs().empty())
        error(*_contract.definedStructs().front(), "User-defined types not supported.");
    if (!_contract.definedEnums().empty())
        error(*_contract.definedEnums().front(), "User-defined types not supported.");
    if (!_contract.events().empty())
        error(*_contract.events().front(), "Events not supported.");
    if (!_contract.functionModifiers().empty())
        error(*_contract.functionModifiers().front(), "Modifiers not supported.");

    ASTNode::listAccept(_contract.definedFunctions(), *this);

    return false;
}

void Why3Translator::endVisit(ContractDefinition const&)
{
    m_currentContract.reset();
    unindent();
    addLine("end");
}

bool Why3Translator::visit(FunctionDefinition const& _function)
{
    if (!_function.isImplemented())
    {
        error(_function, "Unimplemented functions not supported.");
        return false;
    }
    if (_function.name().empty())
    {
        error(_function, "Fallback functions not supported.");
        return false;
    }
    if (!_function.modifiers().empty())
    {
        error(_function, "Modifiers not supported.");
        return false;
    }

    m_localVariables.clear();
    for (auto const& var: _function.parameters())
        m_localVariables[var->name()] = var.get();
    for (auto const& var: _function.returnParameters())
        m_localVariables[var->name()] = var.get();
    for (auto const& var: _function.localVariables())
        m_localVariables[var->name()] = var;

    add("let rec _" + _function.name());
    add(" (this: account)");
    for (auto const& param: _function.parameters())
    {
        string paramType;
        try
        {
            paramType = toFormalType(*param->annotation().type);
        }
        catch (NoFormalType &err)
        {
            string const* typeName = boost::get_error_info<errinfo_noFormalTypeFrom>(err);
            error(*param, "Parameter type \"" + (typeName ? *typeName : "") + "\" not supported.");
        }
        if (param->name().empty())
            error(*param, "Anonymous function parameters not supported.");
        add(" (arg_" + param->name() + ": " + paramType + ")");
    }
    add(":");

    indent();
    indent();
    string retString = "(";
    for (auto const& retParam: _function.returnParameters())
    {
        string paramType;
        try
        {
            paramType = toFormalType(*retParam->annotation().type);
        }
        catch (NoFormalType &err)
        {
            string const* typeName = boost::get_error_info<errinfo_noFormalTypeFrom>(err);
            error(*retParam, "Parameter type " + (typeName ? *typeName : "") + " not supported.");
        }
        if (retString.size() != 1)
            retString += ", ";
        retString += paramType;
    }
    add(retString + ")");
    unindent();

    addSourceFromDocStrings(_function.annotation());
    if (!m_currentContract.contract)
        error(_function, "Only functions inside contracts allowed.");
    addSourceFromDocStrings(m_currentContract.contract->annotation());

    if (_function.isDeclaredConst())
        addLine("ensures { (old this) = this }");
    else
        addLine("writes { this }");

    addLine("=");

    // store the prestate in the case we need to revert
    addLine("let prestate = {balance = this.balance; storage = " + copyOfStorage() + "} in ");

    // initialise local variables
    for (auto const& variable: _function.parameters())
        addLine("let _" + variable->name() + " = ref arg_" + variable->name() + " in");
    for (auto const& variable: _function.returnParameters())
    {
        if (variable->name().empty())
            error(*variable, "Unnamed return variables not yet supported.");
        string varType;
        try
        {
            varType = toFormalType(*variable->annotation().type);
        }
        catch (NoFormalType &err)
        {
            string const* typeNamePtr = boost::get_error_info<errinfo_noFormalTypeFrom>(err);
            error(*variable, "Type " + (typeNamePtr ? *typeNamePtr : "") + "in return parameter not yet supported.");
        }
        addLine("let _" + variable->name() + ": ref " + varType + " = ref (of_int 0) in");
    }
    for (VariableDeclaration const* variable: _function.localVariables())
    {
        if (variable->name().empty())
            error(*variable, "Unnamed variables not yet supported.");
        string varType;
        try
        {
            varType = toFormalType(*variable->annotation().type);
        }
        catch (NoFormalType &err)
        {
            string const* typeNamePtr = boost::get_error_info<errinfo_noFormalTypeFrom>(err);
            error(*variable, "Type " + (typeNamePtr ? *typeNamePtr : "") + "in variable declaration not yet supported.");
        }
        addLine("let _" + variable->name() + ": ref " + varType + " = ref (of_int 0) in");
    }
    addLine("try");

    _function.body().accept(*this);
    add(";");
    addLine("raise Return");

    string retVals;
    for (auto const& variable: _function.returnParameters())
    {
        if (!retVals.empty())
            retVals += ", ";
        retVals += "!_" + variable->name();
    }
    addLine("with Return -> (" + retVals + ") |");
    string reversion = "     Revert -> this.balance <- prestate.balance; ";
    for (auto const* variable: m_currentContract.stateVariables)
        reversion += "this.storage._" + variable->name() + " <- prestate.storage._" + variable->name() + "; ";
    //@TODO in case of reversion the return values are wrong - we need to change the
    // return type to include a bool to signify if an exception was thrown.
    reversion += "(" + retVals + ")";
    addLine(reversion);
    unindent();
    addLine("end");
    addLine("");
    return false;
}

void Why3Translator::endVisit(FunctionDefinition const&)
{
    m_localVariables.clear();
}

bool Why3Translator::visit(Block const& _node)
{
    addSourceFromDocStrings(_node.annotation());
    add("begin");
    indent();
    for (size_t i = 0; i < _node.statements().size(); ++i)
    {
        _node.statements()[i]->accept(*this);
        if (i != _node.statements().size() - 1)
        {
            auto it = m_lines.end() - 1;
            while (it != m_lines.begin() && it->contents.empty())
                --it;
            if (!boost::algorithm::ends_with(it->contents, "begin"))
                it->contents += ";";
        }
        newLine();
    }
    unindent();
    add("end");
    return false;
}

bool Why3Translator::visit(IfStatement const& _node)
{
    addSourceFromDocStrings(_node.annotation());

    add("if ");
    _node.condition().accept(*this);
    add(" then");
    visitIndentedUnlessBlock(_node.trueStatement());
    if (_node.falseStatement())
    {
        newLine();
        add("else");
        visitIndentedUnlessBlock(*_node.falseStatement());
    }
    return false;
}

bool Why3Translator::visit(WhileStatement const& _node)
{
    addSourceFromDocStrings(_node.annotation());

    // Why3 does not appear to support do-while loops,
    // so we will simulate them by performing a while
    // loop with the body prepended once.

    if (_node.isDoWhile())
    {
        visitIndentedUnlessBlock(_node.body());
        newLine();
    }

    add("while ");
    _node.condition().accept(*this);
    newLine();
    add("do");
    visitIndentedUnlessBlock(_node.body());
    add("done");
    return false;
}

bool Why3Translator::visit(Return const& _node)
{
    addSourceFromDocStrings(_node.annotation());

    if (_node.expression())
    {
        solAssert(!!_node.annotation().functionReturnParameters, "");
        auto const& params = _node.annotation().functionReturnParameters->parameters();
        if (params.size() != 1)
        {
            error(_node, "Directly returning tuples not supported. Rather assign to return variable.");
            return false;
        }
        add("begin _" + params.front()->name() + " := ");
        _node.expression()->accept(*this);
        add("; raise Return end");
    }
    else
        add("raise Return");
    return false;
}

bool Why3Translator::visit(Throw const& _node)
{
    addSourceFromDocStrings(_node.annotation());
    add("raise Revert");
    return false;
}

bool Why3Translator::visit(VariableDeclarationStatement const& _node)
{
    addSourceFromDocStrings(_node.annotation());

    if (_node.declarations().size() != 1)
    {
        error(_node, "Multiple variables not supported.");
        return false;
    }
    if (_node.initialValue())
    {
        add("_" + _node.declarations().front()->name() + " := ");
        _node.initialValue()->accept(*this);
    }
    return false;
}

bool Why3Translator::visit(ExpressionStatement const& _node)
{
    addSourceFromDocStrings(_node.annotation());
    return true;
}

bool Why3Translator::visit(Assignment const& _node)
{
    if (_node.assignmentOperator() != Token::Assign)
        error(_node, "Compound assignment not supported.");

    _node.leftHandSide().accept(*this);

    add(m_currentLValueIsRef ? " := " : " <- ");
    _node.rightHandSide().accept(*this);

    return false;
}

bool Why3Translator::visit(TupleExpression const& _node)
{
    if (_node.components().size() != 1)
        error(_node, "Only tuples with exactly one component supported.");
    add("(");
    return true;
}

bool Why3Translator::visit(UnaryOperation const& _unaryOperation)
{
    try
    {
        toFormalType(*_unaryOperation.annotation().type);
    }
    catch (NoFormalType &err)
    {
        string const* typeNamePtr = boost::get_error_info<errinfo_noFormalTypeFrom>(err);
        error(_unaryOperation, "Type \"" + (typeNamePtr ? *typeNamePtr : "") + "\" supported in unary operation.");
    }

    switch (_unaryOperation.getOperator())
    {
    case Token::Not: // !
        add("(not ");
        break;
    default:
        error(_unaryOperation, "Operator not supported.");
        break;
    }

    _unaryOperation.subExpression().accept(*this);
    add(")");

    return false;
}

bool Why3Translator::visit(BinaryOperation const& _binaryOperation)
{
    Expression const& leftExpression = _binaryOperation.leftExpression();
    Expression const& rightExpression = _binaryOperation.rightExpression();
    solAssert(!!_binaryOperation.annotation().commonType, "");
    Type const& commonType = *_binaryOperation.annotation().commonType;
    Token::Value const c_op = _binaryOperation.getOperator();

    if (commonType.category() == Type::Category::RationalNumber)
    {
        auto const& constantNumber = dynamic_cast<RationalNumberType const&>(commonType);
        if (constantNumber.isFractional())
            error(_binaryOperation, "Fractional numbers not supported.");
        else
            add("(of_int " + toString(commonType.literalValue(nullptr)) + ")");
        return false;
    }
    static const map<Token::Value, char const*> optrans({
        {Token::And, " && "},
        {Token::Or, " || "},
        {Token::BitOr, " lor "},
        {Token::BitXor, " lxor "},
        {Token::BitAnd, " land "},
        {Token::Add, " + "},
        {Token::Sub, " - "},
        {Token::Mul, " * "},
        {Token::Div, " / "},
        {Token::Mod, " mod "},
        {Token::Equal, " = "},
        {Token::NotEqual, " <> "},
        {Token::LessThan, " < "},
        {Token::GreaterThan, " > "},
        {Token::LessThanOrEqual, " <= "},
        {Token::GreaterThanOrEqual, " >= "}
    });
    if (!optrans.count(c_op))
    {
        error(_binaryOperation, "Operator not supported.");
        return true;
    }

    add("(");
    leftExpression.accept(*this);
    add(optrans.at(c_op));
    rightExpression.accept(*this);
    add(")");

    return false;
}

bool Why3Translator::visit(FunctionCall const& _node)
{
    if (_node.annotation().isTypeConversion || _node.annotation().isStructConstructorCall)
    {
        error(_node, "Only ordinary function calls supported.");
        return true;
    }
    FunctionType const& function = dynamic_cast<FunctionType const&>(*_node.expression().annotation().type);
    switch (function.location())
    {
    case FunctionType::Location::AddMod:
    case FunctionType::Location::MulMod:
    {
        //@todo require that third parameter is not zero
        add("(of_int (mod (Int.(");
        add(function.location() == FunctionType::Location::AddMod ? "+" : "*");
        add(") (to_int ");
        _node.arguments().at(0)->accept(*this);
        add(") (to_int ");
        _node.arguments().at(1)->accept(*this);
        add(")) (to_int ");
        _node.arguments().at(2)->accept(*this);
        add(")))");
        return false;
    }
    case FunctionType::Location::Internal:
    {
        if (!_node.names().empty())
        {
            error(_node, "Function calls with named arguments not supported.");
            return true;
        }

        //@TODO check type conversions

        add("(");
        _node.expression().accept(*this);
        add(" state");
        for (auto const& arg: _node.arguments())
        {
            add(" ");
            arg->accept(*this);
        }
        add(")");
        return false;
    }
    case FunctionType::Location::Bare:
    {
        if (!_node.arguments().empty())
        {
            error(_node, "Function calls with named arguments not supported.");
            return true;
        }

        add("(");
        indent();
        add("let amount = 0 in ");
        _node.expression().accept(*this);
        addLine("if amount <= this.balance then");
        indent();
        addLine("let balance_precall = this.balance in");
        addLine("begin");
        indent();
        addLine("this.balance <- this.balance - amount;");
        addLine("if not (external_call this) then begin this.balance = balance_precall; false end else true");
        unindent();
        addLine("end");
        unindent();
        addLine("else false");

        unindent();
        add(")");
        return false;
    }
    case FunctionType::Location::SetValue:
    {
        add("let amount = ");
        solAssert(_node.arguments().size() == 1, "");
        _node.arguments()[0]->accept(*this);
        add(" in ");
        return false;
    }
    default:
        error(_node, "Only internal function calls supported.");
        return true;
    }
}

bool Why3Translator::visit(MemberAccess const& _node)
{
    if (
        _node.expression().annotation().type->category() == Type::Category::Array &&
        _node.memberName() == "length" &&
        !_node.annotation().lValueRequested
    )
    {
        add("(of_int ");
        _node.expression().accept(*this);
        add(".length");
        add(")");
    }
    else if (
        _node.memberName() == "call" &&
        *_node.expression().annotation().type == IntegerType(160, IntegerType::Modifier::Address)
    )
    {
        // Do nothing, do not even visit the address because this will be an external call
        //@TODO ensure that the expression itself does not have side-effects
        return false;
    }
    else
        error(_node, "Member access: Only call and array length supported.");
    return false;
}

bool Why3Translator::visit(IndexAccess const& _node)
{
    auto baseType = dynamic_cast<ArrayType const*>(_node.baseExpression().annotation().type.get());
    if (!baseType)
    {
        error(_node, "Index access only supported for arrays.");
        return true;
    }
    if (_node.annotation().lValueRequested)
    {
        error(_node, "Assignment to array elements not supported.");
        return true;
    }
    add("(");
    _node.baseExpression().accept(*this);
    add("[to_int ");
    _node.indexExpression()->accept(*this);
    add("]");
    add(")");

    return false;
}

bool Why3Translator::visit(Identifier const& _identifier)
{
    Declaration const* declaration = _identifier.annotation().referencedDeclaration;
    if (FunctionDefinition const* functionDef = dynamic_cast<FunctionDefinition const*>(declaration))
        add("_" + functionDef->name());
    else if (auto variable = dynamic_cast<VariableDeclaration const*>(declaration))
    {
        bool isStateVar = isStateVariable(variable);
        bool lvalue = _identifier.annotation().lValueRequested;
        if (isStateVar)
            add("this.storage.");
        else if (!lvalue)
            add("!(");
        add("_" + variable->name());
        if (!isStateVar && !lvalue)
            add(")");
        m_currentLValueIsRef = !isStateVar;
    }
    else
        error(_identifier, "Not supported.");
    return false;
}

bool Why3Translator::visit(Literal const& _literal)
{
    TypePointer type = _literal.annotation().type;
    switch (type->category())
    {
    case Type::Category::Bool:
        if (type->literalValue(&_literal) == 0)
            add("false");
        else
            add("true");
        break;
    case Type::Category::RationalNumber:
    {
        auto const& constantNumber = dynamic_cast<RationalNumberType const&>(*type);
        if (constantNumber.isFractional())
            error(_literal, "Fractional numbers not supported.");
        else
            add("(of_int " + toString(type->literalValue(&_literal)) + ")");
        break;
    }
    default:
        error(_literal, "Not supported.");
    }
    return false;
}

bool Why3Translator::visit(PragmaDirective const& _pragma)
{
    if (_pragma.tokens().empty())
        error(_pragma, "Not supported");
    else if (_pragma.literals().empty())
        error(_pragma, "Not supported");
    else if (_pragma.literals()[0] != "solidity")
        error(_pragma, "Not supported");
    else if (_pragma.tokens()[0] != Token::Identifier)
        error(_pragma, "A literal 'solidity' is not an identifier.  Strange");

    return false;
}

bool Why3Translator::isStateVariable(VariableDeclaration const* _var) const
{
    return contains(m_currentContract.stateVariables, _var);
}

bool Why3Translator::isStateVariable(string const& _name) const
{
    for (auto const& var: m_currentContract.stateVariables)
        if (var->name() == _name)
            return true;
    return false;
}

bool Why3Translator::isLocalVariable(VariableDeclaration const* _var) const
{
    for (auto const& var: m_localVariables)
        if (var.second == _var)
            return true;
    return false;
}

bool Why3Translator::isLocalVariable(string const& _name) const
{
    return m_localVariables.count(_name);
}

string Why3Translator::copyOfStorage() const
{
    if (m_currentContract.stateVariables.empty())
        return "()";
    string ret = "{";
    bool first = true;
    for (auto const* variable: m_currentContract.stateVariables)
    {
        if (first)
            first = false;
        else
            ret += "; ";
        ret += "_" + variable->name() + " = this.storage._" + variable->name();
    }
    return ret + "}";
}

void Why3Translator::visitIndentedUnlessBlock(Statement const& _statement)
{
    bool isBlock = !!dynamic_cast<Block const*>(&_statement);
    if (isBlock)
        newLine();
    else
        indent();
    _statement.accept(*this);
    if (isBlock)
        newLine();
    else
        unindent();
}

void Why3Translator::addSourceFromDocStrings(DocumentedAnnotation const& _annotation)
{
    auto why3Range = _annotation.docTags.equal_range("why3");
    for (auto i = why3Range.first; i != why3Range.second; ++i)
        addLine(transformVariableReferences(i->second.content));
}

string Why3Translator::transformVariableReferences(string const& _annotation)
{
    string ret;
    auto pos = _annotation.begin();
    while (true)
    {
        auto hash = find(pos, _annotation.end(), '#');
        ret.append(pos, hash);
        if (hash == _annotation.end())
            break;

        auto hashEnd = find_if(hash + 1, _annotation.end(), [](char _c)
        {
            return
                (_c != '_' && _c != '$') &&
                !('a' <= _c && _c <= 'z') &&
                !('A' <= _c && _c <= 'Z') &&
                !('0' <= _c && _c <= '9');
        });
        string varName(hash + 1, hashEnd);
        if (isLocalVariable(varName))
            ret += "(!_" + varName + ")";
        else if (isStateVariable(varName))
            ret += "(this.storage._" + varName + ")";
        //@todo return variables
        else
            ret.append(hash, hashEnd);

        pos = hashEnd;
    }
    return ret;
}

void Why3Translator::appendPreface()
{
    m_lines.push_back(Line{R"(
module UInt256
    use import mach.int.Unsigned
    type uint256
    constant max_uint256: int = 0xffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff
    clone export mach.int.Unsigned with
        type t = uint256,
        constant max = max_uint256
end

module Address
    use import mach.int.Unsigned
    type address
    constant max_address: int = 0xffffffffffffffffffffffffffffffffffffffff (* 160 bit = 40 f's *)
    clone export mach.int.Unsigned with
        type t = address,
        constant max = max_address
end
   )", 0});
}