Processor.cpp

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#include <Ark/Compiler/Macros/Processor.hpp>
 
#include <utility>
#include <algorithm>
#include <cassert>
#include <ranges>
#include <sstream>
#include <fmt/core.h>
 
#include <Ark/Constants.hpp>
#include <Ark/Error/Exceptions.hpp>
#include <Ark/Builtins/Builtins.hpp>
#include <Ark/Compiler/Macros/Executor.hpp>
#include <Ark/Compiler/Macros/Executors/Symbol.hpp>
#include <Ark/Compiler/Macros/Executors/Function.hpp>
#include <Ark/Compiler/Macros/Executors/Conditional.hpp>
 
namespace Ark::internal
{
    MacroProcessor::MacroProcessor(const unsigned debug) noexcept :
        Pass("MacroProcessor", debug)
    {
        // create executors pipeline
        m_conditional_executor = std::make_shared<ConditionalExecutor>(this);
        m_executors.emplace_back(std::make_shared<SymbolExecutor>(this));
        m_executors.emplace_back(m_conditional_executor);
        m_executors.emplace_back(std::make_shared<FunctionExecutor>(this));
    }
 
    void MacroProcessor::process(const Node& ast)
    {
        m_logger.debug("Processing macros...");
        m_logger.traceStart("process");
 
        // to be able to modify it
        m_ast = ast;
        processNode(m_ast, 0);
 
        m_logger.traceEnd();
        m_logger.trace("AST after processing macros");
        if (m_logger.shouldTrace())
            m_ast.debugPrint(std::cout) << '\n';
    }
 
    const Node& MacroProcessor::ast() const noexcept
    {
        return m_ast;
    }
 
    void MacroProcessor::handleMacroNode(Node& node, const unsigned depth)
    {
        // a macro needs at least 2 nodes, name + value is the minimal form
        // this is guaranteed by the parser
        assert(node.constList().size() >= 2 && "Invalid macro, missing value");
 
        const Node& first_node = node.list()[0];
 
        // (macro name value)
        if (node.constList().size() == 2)
        {
            assert(first_node.nodeType() == NodeType::Symbol && "Can not define a macro without a symbol");
            // processNode is needed here to correctly expand macros when we have something like
            //   (macro arg_bloc (__suffix-dup arg length))                                    /
            //   (macro all_args (__replace_placeholders [arg_bloc] ...args))  <--------------*
            // otherwise, 'arg_bloc' isn't expanded here, and we get in trouble
            processNode(node.list()[1], depth + 1);
            applyMacro(node.list()[1], depth + 1);
            node.list()[1] = evaluate(node.list()[1], depth + 1, true);
            m_macros.back().add(first_node.string(), node);
        }
        // (macro name (args) body)
        else if (node.constList().size() == 3 && first_node.nodeType() == NodeType::Symbol)
        {
            assert(node.constList()[1].nodeType() == NodeType::List && "Invalid macro argument's list");
            m_macros.back().add(first_node.string(), node);
        }
        // in case we had a conditional, we need to evaluate and expand it
        else if (m_conditional_executor->canHandle(node))
            m_conditional_executor->applyMacro(node, depth + 1);
    }
 
    // todo find a better way to do this
    void MacroProcessor::registerFuncDef(const Node& node)
    {
        if (node.nodeType() == NodeType::List && node.constList().size() == 3 && node.constList()[0].nodeType() == NodeType::Keyword)
        {
            const Keyword kw = node.constList()[0].keyword();
            // checking for function definition, which can occur only inside an assignment node
            if (kw != Keyword::Let && kw != Keyword::Mut && kw != Keyword::Set)
                return;
 
            const Node inner = node.constList()[2];
            if (inner.nodeType() != NodeType::List)
                return;
 
            if (!inner.constList().empty() && inner.constList()[0].nodeType() == NodeType::Keyword && inner.constList()[0].keyword() == Keyword::Fun)
            {
                const Node symbol = node.constList()[1];
                if (symbol.nodeType() == NodeType::Symbol)
                    m_defined_functions.emplace(symbol.string(), inner.constList()[1]);
                else
                    throwMacroProcessingError(fmt::format("Can not use a {} to define a variable", typeToString(symbol)), symbol);
            }
        }
    }
 
    void MacroProcessor::processNode(Node& node, unsigned depth, const bool is_processing_namespace)
    {
        if (depth >= MaxMacroProcessingDepth)
            throwMacroProcessingError(
                fmt::format(
                    "Max recursion depth reached ({}). You most likely have a badly defined recursive macro calling itself without a proper exit condition",
                    MaxMacroProcessingDepth),
                node);
 
        if (node.nodeType() == NodeType::List)
        {
            bool has_created = false;
            std::size_t i = 0;
            while (i < node.list().size())
            {
                const std::size_t pos = i;
                Node& child = node.list()[pos];
                const bool had_begin = isBeginNode(child);
                bool added_begin = false;
 
                if (child.nodeType() == NodeType::Macro)
                {
                    // create a scope only if needed
                    if ((!m_macros.empty() && !m_macros.back().empty() && m_macros.back().depth() < depth && !is_processing_namespace) ||
                        (!has_created && !is_processing_namespace) ||
                        (m_macros.empty() && is_processing_namespace))
                    {
                        has_created = true;
                        m_macros.emplace_back(depth);
                    }
 
                    handleMacroNode(child, depth);
                    if (child.nodeType() != NodeType::Macro)
                        evaluate(child, depth);
                    added_begin = isBeginNode(child) && !had_begin;
                }
                else  // running on non-macros
                {
                    applyMacro(child, 0);
                    added_begin = isBeginNode(child) && !had_begin;
 
                    if (child.nodeType() == NodeType::Unused)
                        node.list().erase(node.constList().begin() + static_cast<std::vector<Node>::difference_type>(pos));
                    else if (!added_begin)
                        // Go forward only if it isn't a macro, because we delete macros
                        // while running on the AST. Also, applying a macro can result in
                        // nodes being marked unused, and delete them immediately. When
                        // that happens, we can't increment i, otherwise we delete a node,
                        // advance, resulting in a node being skipped!
                        ++i;
 
                    // process subnodes if any
                    if (node.nodeType() == NodeType::List && pos < node.constList().size())
                    {
                        processNode(child, depth + 1);
                        // needed if we created a function node from a macro
                        registerFuncDef(child);
                    }
                }
 
                if (pos < node.constList().size())
                {
                    // if we now have a surrounding (begin ...) and didn't have one before, remove it
                    if (added_begin)
                        removeBegin(node, pos);
                    // if there is an unused node or a leftover macro need, we need to get rid of it in the final ast
                    else if (child.nodeType() == NodeType::Macro || child.nodeType() == NodeType::Unused)
                        node.list().erase(node.constList().begin() + static_cast<std::vector<Node>::difference_type>(pos));
                }
            }
 
            // delete a scope only if needed
            if (!m_macros.empty() && m_macros.back().depth() == depth && !is_processing_namespace)
                m_macros.pop_back();
        }
        else if (node.nodeType() == NodeType::Namespace)
        {
            Node& namespace_ast = *node.arkNamespace().ast;
            // We have to use depth - 1 because it was incremented previously, as a namespace node
            // must be in a list node. Then depth - 1 is safe as depth is at least 1.
            // Using a decreased value of depth ensures that macros are stored in the correct scope,
            // and not deleted when the namespace traversal ends.
            processNode(namespace_ast, depth - 1, /* is_processing_namespace= */ true);
        }
    }
 
    bool MacroProcessor::applyMacro(Node& node, const unsigned depth)
    {
        if (depth > MaxMacroProcessingDepth)
            throwMacroProcessingError(
                fmt::format(
                    "Max macro processing depth reached ({}). You may have a macro trying to evaluate itself, try splitting your code in multiple nodes.",
                    MaxMacroProcessingDepth),
                node);
 
        for (const auto& executor : m_executors)
        {
            if (executor->canHandle(node))
            {
                m_macros_being_applied.push_back(executor->macroNode(node));
                const bool applied = executor->applyMacro(node, depth);
                m_macros_being_applied.pop_back();
 
                if (applied)
                    return true;
            }
        }
        return false;
    }
 
    void MacroProcessor::checkMacroArgCountEq(const Node& node, std::size_t expected, const std::string& name, const bool is_expansion, const std::string& kind) const
    {
        const std::size_t argcount = node.constList().size();
        if (argcount != expected + 1)
        {
            if (is_expansion)
                throwMacroProcessingError(
                    fmt::format(
                        "When expanding `{}' inside a macro, got {} argument{}, expected {}",
                        name,
                        argcount - 1,
                        argcount > 2 ? "s" : "",
                        expected),
                    node);
            else
                throwMacroProcessingError(
                    fmt::format(
                        "Interpreting a `{}'{} with {} argument{}, expected {}.",
                        name,
                        kind.empty() ? kind : " " + kind,
                        argcount - 1,
                        argcount > 2 ? "s" : "",
                        expected),
                    node);
        }
    }
 
    void MacroProcessor::checkMacroArgCountGe(const Node& node, std::size_t expected, const std::string& name, const std::string& kind) const
    {
        const std::size_t argcount = node.constList().size();
        if (argcount < expected + 1)
            throwMacroProcessingError(
                fmt::format(
                    "Interpreting a `{}'{} with {} argument{}, expected at least {}.",
                    name,
                    kind.empty() ? kind : " " + kind,
                    argcount - 1,
                    argcount > 2 ? "s" : "",
                    expected),
                node);
    }
 
    Node MacroProcessor::evaluate(Node& node, const unsigned depth, const bool is_not_body)
    {
        if (node.nodeType() == NodeType::Symbol)
        {
            const Node* macro = findNearestMacro(node.string());
            if (macro != nullptr && macro->constList().size() == 2)
                return macro->constList()[1];
            return node;
        }
        if (node.nodeType() == NodeType::List && !node.constList().empty() && node.list()[0].nodeType() == NodeType::Symbol)
        {
            const std::string& name = node.list()[0].string();
            const std::size_t argcount = node.list().size() - 1;
 
            if (const Node* macro = findNearestMacro(name); macro != nullptr)
            {
                applyMacro(node.list()[0], depth + 1);
                if (node.list()[0].nodeType() == NodeType::Unused)
                    node.list().erase(node.constList().begin());
            }
            else if (name == "=" && is_not_body)
            {
                checkMacroArgCountEq(node, 2, "=", /* is_expansion= */ false, "condition");
                const Node one = evaluate(node.list()[1], depth + 1, is_not_body);
                const Node two = evaluate(node.list()[2], depth + 1, is_not_body);
                return (one == two) ? getTrueNode() : getFalseNode();
            }
            else if (name == "!=" && is_not_body)
            {
                checkMacroArgCountEq(node, 2, "!=", /* is_expansion= */ false, "condition");
                const Node one = evaluate(node.list()[1], depth + 1, is_not_body);
                const Node two = evaluate(node.list()[2], depth + 1, is_not_body);
                return (one != two) ? getTrueNode() : getFalseNode();
            }
            else if (name == "<" && is_not_body)
            {
                checkMacroArgCountEq(node, 2, "<", /* is_expansion= */ false, "condition");
                const Node one = evaluate(node.list()[1], depth + 1, is_not_body);
                const Node two = evaluate(node.list()[2], depth + 1, is_not_body);
                return (one < two) ? getTrueNode() : getFalseNode();
            }
            else if (name == ">" && is_not_body)
            {
                checkMacroArgCountEq(node, 2, ">", /* is_expansion= */ false, "condition");
                const Node one = evaluate(node.list()[1], depth + 1, is_not_body);
                const Node two = evaluate(node.list()[2], depth + 1, is_not_body);
                return !(one < two) && (one != two) ? getTrueNode() : getFalseNode();
            }
            else if (name == "<=" && is_not_body)
            {
                checkMacroArgCountEq(node, 2, "<=", /* is_expansion= */ false, "condition");
                const Node one = evaluate(node.list()[1], depth + 1, is_not_body);
                const Node two = evaluate(node.list()[2], depth + 1, is_not_body);
                return one < two || one == two ? getTrueNode() : getFalseNode();
            }
            else if (name == ">=" && is_not_body)
            {
                checkMacroArgCountEq(node, 2, ">=", /* is_expansion= */ false, "condition");
                const Node one = evaluate(node.list()[1], depth + 1, is_not_body);
                const Node two = evaluate(node.list()[2], depth + 1, is_not_body);
                return !(one < two) ? getTrueNode() : getFalseNode();
            }
            else if (name == "+" && is_not_body)
            {
                checkMacroArgCountGe(node, 2, "+", "operator");
                double v = 0.0;
                for (auto& child : node.list() | std::ranges::views::drop(1))
                {
                    Node ev = evaluate(child, depth + 1, is_not_body);
                    if (ev.nodeType() != NodeType::Number)
                        return node;
                    v += ev.number();
                }
                return Node(v);
            }
            else if (name == "-" && is_not_body)
            {
                checkMacroArgCountGe(node, 2, "-", "operator");
                const Node one = evaluate(node.list()[1], depth + 1, is_not_body);
                if (one.nodeType() != NodeType::Number)
                    return node;
 
                double v = one.number();
                for (auto& child : node.list() | std::ranges::views::drop(2))
                {
                    Node ev = evaluate(child, depth + 1, is_not_body);
                    if (ev.nodeType() != NodeType::Number)
                        return node;
                    v -= ev.number();
                }
                return Node(v);
            }
            else if (name == "*" && is_not_body)
            {
                checkMacroArgCountGe(node, 2, "*", "operator");
                double v = 1.0;
                for (auto& child : node.list() | std::ranges::views::drop(1))
                {
                    Node ev = evaluate(child, depth + 1, is_not_body);
                    if (ev.nodeType() != NodeType::Number)
                        return node;
                    v *= ev.number();
                }
                return Node(v);
            }
            else if (name == "/" && is_not_body)
            {
                checkMacroArgCountGe(node, 2, "/", "operator");
                const Node one = evaluate(node.list()[1], depth + 1, is_not_body);
                if (one.nodeType() != NodeType::Number)
                    return node;
 
                double v = one.number();
                for (auto& child : node.list() | std::ranges::views::drop(2))
                {
                    Node ev = evaluate(child, depth + 1, is_not_body);
                    if (ev.nodeType() != NodeType::Number)
                        return node;
                    v /= ev.number();
                }
                return Node(v);
            }
            else if (name == "not" && is_not_body)
            {
                checkMacroArgCountEq(node, 1, "not", /* is_expansion= */ false, "condition");
                return (!isTruthy(evaluate(node.list()[1], depth + 1, is_not_body))) ? getTrueNode() : getFalseNode();
            }
            else if (name == Language::And && is_not_body)
            {
                if (node.list().size() < 3)
                    throwMacroProcessingError(fmt::format("Interpreting a `{}' chain with {} arguments, expected at least 2.", Language::And, argcount), node);
 
                for (std::size_t i = 1, end = node.list().size(); i < end; ++i)
                {
                    if (!isTruthy(evaluate(node.list()[i], depth + 1, is_not_body)))
                        return getFalseNode();
                }
                return getTrueNode();
            }
            else if (name == Language::Or && is_not_body)
            {
                if (node.list().size() < 3)
                    throwMacroProcessingError(fmt::format("Interpreting an `{}' chain with {} arguments, expected at least 2.", Language::Or, argcount), node);
 
                for (std::size_t i = 1, end = node.list().size(); i < end; ++i)
                {
                    if (isTruthy(evaluate(node.list()[i], depth + 1, is_not_body)))
                        return getTrueNode();
                }
                return getFalseNode();
            }
            else if (name == "$len")
            {
                checkMacroArgCountEq(node, 1, "$len", true);
                Node& lst = node.list()[1];
                checkMacroTypeError("$len", "node", NodeType::List, lst);
 
                if (!lst.list().empty() && lst.list()[0] == getListNode())
                    node.updateValueAndType(Node(static_cast<long>(lst.list().size()) - 1));
                else
                    node.updateValueAndType(Node(static_cast<long>(lst.list().size())));
            }
            else if (name == "$empty?")
            {
                checkMacroArgCountEq(node, 1, "$empty?", true);
 
                if (Node& lst = node.list()[1]; lst.nodeType() == NodeType::List)
                {
                    // only apply len at compile time if we can
                    if (!lst.list().empty() && lst.list()[0] == getListNode())
                        node.updateValueAndType(lst.list().size() - 1 == 0 ? getTrueNode() : getFalseNode());
                    else
                        node.updateValueAndType(lst.list().empty() ? getTrueNode() : getFalseNode());
                }
                else if (lst == getNilNode())
                    node.updateValueAndType(getTrueNode());
            }
            else if (name == "$at")
            {
                checkMacroArgCountEq(node, 2, "$at");
 
                Node sublist = evaluate(node.list()[1], depth + 1, is_not_body);
                const Node idx = evaluate(node.list()[2], depth + 1, is_not_body);
 
                checkMacroTypeError("$at", "list", NodeType::List, sublist);
                checkMacroTypeError("$at", "index", NodeType::Number, idx);
 
                const std::size_t size = sublist.list().size();
                std::size_t real_size = size;
                long num_idx = static_cast<long>(idx.number());
 
                // if the first node is the function call to "list", don't count it
                if (size > 0 && sublist.list()[0] == getListNode())
                {
                    real_size--;
                    if (num_idx >= 0)
                        ++num_idx;
                }
 
                Node output;
                if (num_idx >= 0 && std::cmp_less(num_idx, size))
                    output = sublist.list()[static_cast<std::size_t>(num_idx)];
                else if (const auto c = static_cast<long>(size) + num_idx; num_idx < 0 && std::cmp_less(c, size) && c >= 0)
                    output = sublist.list()[static_cast<std::size_t>(c)];
                else
                    throwMacroProcessingError(fmt::format("Index ({}) out of range (list size: {})", num_idx, real_size), node);
 
                output.setPositionFrom(node);
                return output;
            }
            else if (name == "$head")
            {
                checkMacroArgCountEq(node, 1, "$head", true);
                Node sublist = node.list()[1];
                checkMacroTypeError("$head", "node", NodeType::List, sublist);
 
                if (!sublist.constList().empty() && sublist.constList()[0] == getListNode())
                {
                    if (sublist.constList().size() > 1)
                    {
                        const Node sublistCopy = sublist.constList()[1];
                        node.updateValueAndType(sublistCopy);
                    }
                    else
                        node.updateValueAndType(getNilNode());
                }
                else if (!sublist.list().empty())
                    node.updateValueAndType(sublist.constList()[0]);
                else
                    node.updateValueAndType(getNilNode());
            }
            else if (name == "$tail")
            {
                checkMacroArgCountEq(node, 1, "$tail", true);
                Node sublist = node.list()[1];
                checkMacroTypeError("$tail", "node", NodeType::List, sublist);
 
                if (!sublist.list().empty() && sublist.list()[0] == getListNode())
                {
                    if (sublist.list().size() > 1)
                    {
                        sublist.list().erase(sublist.constList().begin() + 1);
                        node.updateValueAndType(sublist);
                    }
                    else
                    {
                        node.updateValueAndType(Node(NodeType::List));
                        node.push_back(getListNode());
                    }
                }
                else if (!sublist.list().empty())
                {
                    sublist.list().erase(sublist.constList().begin());
                    sublist.list().insert(sublist.list().begin(), getListNode());
                    node.updateValueAndType(sublist);
                }
                else
                {
                    node.updateValueAndType(Node(NodeType::List));
                    node.push_back(getListNode());
                }
            }
            else if (name == Language::Symcat)
            {
                if (node.list().size() <= 2)
                    throwMacroProcessingError(fmt::format("When expanding `{}', expected at least 2 arguments, got {} arguments", Language::Symcat, argcount), node);
                checkMacroTypeError(Language::Symcat.data(), "symbol", NodeType::Symbol, node.list()[1]);
 
                std::string sym = node.list()[1].string();
 
                for (std::size_t i = 2, end = node.list().size(); i < end; ++i)
                {
                    const Node ev = evaluate(node.list()[i], depth + 1, /* is_not_body */ true);
 
                    switch (ev.nodeType())
                    {
                        case NodeType::Number:
                            // we don't want '.' in identifiers
                            sym += std::to_string(static_cast<long int>(ev.number()));
                            break;
 
                        case NodeType::String:
                        case NodeType::Symbol:
                            sym += ev.string();
                            break;
 
                        default:
                            throwMacroProcessingError(
                                fmt::format(
                                    "When expanding `{}', expected either a Number, String or Symbol, got a {}: {}",
                                    Language::Symcat,
                                    typeToString(ev),
                                    ev.repr()),
                                ev);
                    }
                }
 
                node.setNodeType(NodeType::Symbol);
                node.setString(sym);
            }
            else if (name == Language::Argcount)
            {
                checkMacroArgCountEq(node, 1, Language::Argcount.data(), true);
 
                const Node sym = node.constList()[1];
                if (sym.nodeType() == NodeType::Symbol)
                {
                    if (const auto maybe_func = lookupDefinedFunction(sym.string()); maybe_func.has_value())
                        node.updateValueAndType(Node(static_cast<long>(maybe_func->constList().size())));
                    else
                        throwMacroProcessingError(fmt::format("When expanding `{}', expected a known function name, got unbound variable {}", Language::Argcount, sym.string()), sym);
                }
                else if (sym.nodeType() == NodeType::List && sym.constList().size() == 3 && sym.constList()[0].nodeType() == NodeType::Keyword && sym.constList()[0].keyword() == Keyword::Fun)
                    node.updateValueAndType(Node(static_cast<long>(sym.constList()[1].constList().size())));
                else
                    throwMacroProcessingError(fmt::format("When trying to apply `{}', got a {} instead of a Symbol or Function", Language::Argcount, typeToString(sym)), sym);
            }
            else if (name == Language::Repr)
            {
                checkMacroArgCountEq(node, 1, Language::Repr.data(), true);
 
                const Node arg = node.constList()[1];
                node.updateValueAndType(Node(NodeType::String, arg.repr()));
            }
            else if (name == Language::AsIs)
            {
                if (node.list().size() != 2)
                    throwMacroProcessingError(fmt::format("When expanding `{}', expected one argument, got {} arguments", Language::AsIs, argcount), node);
                return node.constList()[1];
            }
            else if (name == Language::Undef)
            {
                if (node.list().size() != 2)
                    throwMacroProcessingError(fmt::format("When expanding `{}', expected one argument, got {} arguments", Language::Undef, argcount), node);
 
                const Node sym = node.constList()[1];
                if (sym.nodeType() == NodeType::Symbol)
                {
                    deleteNearestMacro(sym.string());
                    node.setNodeType(NodeType::Unused);
                    return node;
                }
 
                throwMacroProcessingError(
                    fmt::format(
                        "When expanding `{}', got a {}. Can not un-define a macro without a valid name",
                        Language::Undef, typeToString(sym)),
                    sym);
            }
            else if (name == Language::Type)
            {
                if (node.list().size() != 2)
                    throwMacroProcessingError(fmt::format("When expanding `{}', expected one argument, got {} arguments", Language::Type, argcount), node);
 
                const Node arg = node.constList()[1];
                node.updateValueAndType(Node(NodeType::String, typeToString(arg)));
            }
        }
 
        if (node.nodeType() == NodeType::List && !node.constList().empty())
        {
            for (auto& child : node.list())
                child.updateValueAndType(evaluate(child, depth + 1, is_not_body));
        }
 
        if (node.nodeType() == NodeType::Spread)
            throwMacroProcessingError(fmt::format("Found an unevaluated spread: `{}'", node.string()), node);
 
        return node;
    }
 
    bool MacroProcessor::isTruthy(const Node& node) const
    {
        if (node.nodeType() == NodeType::Symbol)
        {
            if (node.string() == "true")
                return true;
            if (node.string() == "false" || node.string() == "nil")
                return false;
        }
        else if ((node.nodeType() == NodeType::Number && node.number() != 0.0) || (node.nodeType() == NodeType::String && !node.string().empty()))
            return true;
        else if (node.nodeType() == NodeType::Spread)
            throwMacroProcessingError("Can not determine the truth value of a spread symbol", node);
        return false;
    }
 
    std::optional<Node> MacroProcessor::lookupDefinedFunction(const std::string& name) const
    {
        if (m_defined_functions.contains(name))
            return m_defined_functions.at(name);
        return std::nullopt;
    }
 
    const Node* MacroProcessor::findNearestMacro(const std::string& name) const
    {
        if (m_macros.empty())
            return nullptr;
 
        for (const auto& m_macro : std::ranges::reverse_view(m_macros))
        {
            if (const auto res = m_macro.has(name); res != nullptr)
                return res;
        }
        return nullptr;
    }
 
    void MacroProcessor::deleteNearestMacro(const std::string& name)
    {
        if (m_macros.empty())
            return;
 
        for (auto& m_macro : std::ranges::reverse_view(m_macros))
        {
            if (m_macro.remove(name))
            {
                // stop right here because we found one matching macro
                return;
            }
        }
    }
 
    bool MacroProcessor::isBeginNode(const Node& node)
    {
        return node.nodeType() == NodeType::List &&
            !node.constList().empty() &&
            node.constList()[0].nodeType() == NodeType::Keyword &&
            node.constList()[0].keyword() == Keyword::Begin;
    }
 
    void MacroProcessor::removeBegin(Node& node, const std::size_t i)
    {
        if (node.isListLike() && node.list()[i].nodeType() == NodeType::List && !node.list()[i].list().empty())
        {
            Node lst = node.constList()[i];
            const Node first = lst.constList()[0];
 
            if (first.nodeType() == NodeType::Keyword && first.keyword() == Keyword::Begin)
            {
                const std::size_t previous = i;
 
                for (std::size_t block_idx = 1, end = lst.constList().size(); block_idx < end; ++block_idx)
                    node.list().insert(
                        node.constList().begin() + static_cast<std::vector<Node>::difference_type>(i + block_idx),
                        lst.list()[block_idx]);
 
                node.list().erase(node.constList().begin() + static_cast<std::vector<Node>::difference_type>(previous));
            }
        }
    }
 
    void MacroProcessor::throwMacroProcessingError(const std::string& message, const Node& node) const
    {
        const std::optional<CodeErrorContext> maybe_context = [this]() -> std::optional<CodeErrorContext> {
            if (!m_macros_being_applied.empty())
            {
                const Node& origin = m_macros_being_applied.front();
                return CodeErrorContext(
                    origin.filename(),
                    origin.position(),
                    /* from_macro_expansion= */ true);
            }
            return std::nullopt;
        }();
 
        throw CodeError(message, CodeErrorContext(node.filename(), node.position()), maybe_context);
    }
 
    void MacroProcessor::checkMacroTypeError(const std::string& macro, const std::string& arg, const NodeType expected, const Node& actual) const
    {
        if (actual.nodeType() != expected)
            throwMacroProcessingError(
                fmt::format(
                    "When expanding `{}', expected '{}' to be a {}, got a {}: {}",
                    macro,
                    arg,
                    std::string(nodeTypes[static_cast<std::size_t>(expected)]),
                    typeToString(actual),
                    actual.repr()),
                actual);
    }
}