MalachScript/src/Parser/Lexer/Lexer.cpp

#include "Lexer.hpp"
#include <cmath>
#include <stdexcept>
#include "NumericalLexers.hpp"

namespace MalachScript::Parser {
    const LexToken* Lexer::Lex() {
        auto* first = LexNext();
        if (first->GetKind() == LexTokenKind::EndOfFile) {
            return first;
        }
        auto* last = first;
        while (true) {
            auto* next = LexNext();
            last->SetNext(next);
            last = next;
            if (next->GetKind() == LexTokenKind::EndOfFile) {
                break;
            }
        }
        return first;
    }

    LexToken* Lexer::LexNext() {
        auto start = _position;
        auto c = Consume();
        switch (c) {
            case u8'\0': return Create<LexTokenImpl<LexTokenKind::EndOfFile>>(TextSpan(start, start + 1));
            case u8'*': {
                auto n = Peek();
                if (n == u8'*') {
                    Progress();
                    n = Peek();
                    if (n == u8'=') {
                        Progress();
                        // **=
                        return Create<LexTokenImpl<LexTokenKind::StarStarEqualsSymbol>>(TextSpan(start, start + 3));
                    }
                    // **
                    return Create<LexTokenImpl<LexTokenKind::StarStarSymbol>>(TextSpan(start, start + 2));
                }
                if (n == u8'=') {
                    Progress();
                    // *=
                    return Create<LexTokenImpl<LexTokenKind::StarEqualsSymbol>>(TextSpan(start, start + 2));
                }
                // *
                return Create<LexTokenImpl<LexTokenKind::StarSymbol>>(TextSpan(start, start + 1));
            }
            case u8'/':
                if (Peek() == u8'=') {
                    Progress();
                    // /=
                    return Create<LexTokenImpl<LexTokenKind::SlashEqualsSymbol>>(TextSpan(start, start + 2));
                }
                // /
                return Create<LexTokenImpl<LexTokenKind::SlashSymbol>>(TextSpan(start, start + 1));
            case u8'%':
                if (Peek() == u8'=') {
                    Progress();
                    // %=
                    return Create<LexTokenImpl<LexTokenKind::PercentEqualsSymbol>>(TextSpan(start, start + 2));
                }
                // %
                return Create<LexTokenImpl<LexTokenKind::PercentSymbol>>(TextSpan(start, start + 1));
            case u8'+': {
                auto n = Peek();
                if (n == u8'=') {
                    Progress();
                    // +=
                    return Create<LexTokenImpl<LexTokenKind::PlusEqualsSymbol>>(TextSpan(start, start + 2));
                }
                if (n == u8'+') {
                    Progress();
                    // ++
                    return Create<LexTokenImpl<LexTokenKind::PlusPlusSymbol>>(TextSpan(start, start + 2));
                }
                // +
                return Create<LexTokenImpl<LexTokenKind::PlusSymbol>>(TextSpan(start, start + 1));
            }
            case u8'-': {
                auto n = Peek();
                if (n == u8'=') {
                    Progress();
                    // -=
                    return Create<LexTokenImpl<LexTokenKind::MinusEqualsSymbol>>(TextSpan(start, start + 2));
                }
                if (n == u8'-') {
                    Progress();
                    // --
                    return Create<LexTokenImpl<LexTokenKind::MinusMinusSymbol>>(TextSpan(start, start + 2));
                }
                // -
                return Create<LexTokenImpl<LexTokenKind::MinusSymbol>>(TextSpan(start, start + 1));
            }
            case u8'<': {
                auto n = Peek();
                if (n == u8'=') {
                    Progress();
                    // <=
                    return Create<LexTokenImpl<LexTokenKind::LessThanEqualsSymbol>>(TextSpan(start, start + 2));
                }
                if (n == u8'<') {
                    Progress();
                    if (Peek() == u8'=') {
                        Progress();
                        // <<=
                        return Create<LexTokenImpl<LexTokenKind::LessThanLessThanEqualsSymbol>>(
                            TextSpan(start, start + 3));
                    }
                    // <<
                    return Create<LexTokenImpl<LexTokenKind::LessThanLessThanSymbol>>(TextSpan(start, start + 2));
                }
                // <
                return Create<LexTokenImpl<LexTokenKind::LessThanSymbol>>(TextSpan(start, start + 1));
            }
            case u8'>': {
                auto n = Peek();
                if (n == u8'=') {
                    Progress();
                    // >=
                    return Create<LexTokenImpl<LexTokenKind::GreaterThanEqualsSymbol>>(TextSpan(start, start + 2));
                }
                if (n == u8'>') {
                    Progress();
                    n = Peek();
                    if (n == u8'=') {
                        Progress();
                        // >>=
                        return Create<LexTokenImpl<LexTokenKind::GreaterThanGreaterThanEqualsSymbol>>(
                            TextSpan(start, start + 3));
                    }
                    if (n == u8'>') {
                        Progress();
                        if (Peek() == u8'=') {
                            Progress();
                            // >>>=
                            return Create<LexTokenImpl<LexTokenKind::GreaterThanGreaterThanGreaterThanEqualsSymbol>>(
                                TextSpan(start, start + 4));
                        }
                        // >>>
                        return Create<LexTokenImpl<LexTokenKind::GreaterThanGreaterThanGreaterThanSymbol>>(
                            TextSpan(start, start + 3));
                    }
                    // >>
                    return Create<LexTokenImpl<LexTokenKind::GreaterThanGreaterThanSymbol>>(TextSpan(start, start + 2));
                }
                // >
                return Create<LexTokenImpl<LexTokenKind::GreaterThanSymbol>>(TextSpan(start, start + 1));
            }
            case u8'(': return Create<LexTokenImpl<LexTokenKind::OpenParenthesisSymbol>>(TextSpan(start, start + 1));
            case u8')': return Create<LexTokenImpl<LexTokenKind::CloseParenthesisSymbol>>(TextSpan(start, start + 1));
            case u8'=': {
                if (Peek() == u8'=') {
                    Progress();
                    // ==
                    return Create<LexTokenImpl<LexTokenKind::EqualsEqualsSymbol>>(TextSpan(start, start + 2));
                }
                // =
                return Create<LexTokenImpl<LexTokenKind::EqualsSymbol>>(TextSpan(start, start + 1));
            }
            case u8'!': {
                auto n = Peek();
                if (n == u8'=') {
                    Progress();
                    // !=
                    return Create<LexTokenImpl<LexTokenKind::ExclamationMarkEqualsSymbol>>(TextSpan(start, start + 2));
                }
                if (n == u8'i' && Peek(2) == u8's') {
                    Progress(2);
                    // !is
                    return Create<LexTokenImpl<LexTokenKind::ExclamationMarkIsSymbol>>(TextSpan(start, start + 3));
                }
                // !
                return Create<LexTokenImpl<LexTokenKind::ExclamationMarkSymbol>>(TextSpan(start, start + 1));
            }
            case u8'?': return Create<LexTokenImpl<LexTokenKind::QuestionMarkSymbol>>(TextSpan(start, start + 1));
            case u8':': {
                if (Peek() == u8':') {
                    Progress();
                    // ::
                    return Create<LexTokenImpl<LexTokenKind::ColonColonSymbol>>(TextSpan(start, start + 2));
                }
                // :
                return Create<LexTokenImpl<LexTokenKind::ColonSymbol>>(TextSpan(start, start + 1));
            }
            case u8'&': {
                auto n = Peek();
                if (n == u8'=') {
                    Progress();
                    // &=
                    return Create<LexTokenImpl<LexTokenKind::AmpersandEqualsSymbol>>(TextSpan(start, start + 2));
                }
                if (n == u8'&') {
                    Progress();
                    // &&
                    return Create<LexTokenImpl<LexTokenKind::AmpersandAmpersandSymbol>>(TextSpan(start, start + 2));
                }
                // &
                return Create<LexTokenImpl<LexTokenKind::AmpersandSymbol>>(TextSpan(start, start + 1));
            }
            case u8',': return Create<LexTokenImpl<LexTokenKind::CommaSymbol>>(TextSpan(start, start + 1));
            case u8'{':
                return Create<LexTokenImpl<LexTokenKind::OpenCurlyParenthesisSymbol>>(TextSpan(start, start + 1));
            case u8'}':
                return Create<LexTokenImpl<LexTokenKind::CloseCurlyParenthesisSymbol>>(TextSpan(start, start + 1));
            case u8';': return Create<LexTokenImpl<LexTokenKind::SemicolonSymbol>>(TextSpan(start, start + 1));
            case u8'|': {
                auto n = Peek();
                if (n == u8'=') {
                    Progress();
                    // |=
                    return Create<LexTokenImpl<LexTokenKind::VerticalLineEqualsSymbol>>(TextSpan(start, start + 2));
                }
                if (n == u8'|') {
                    Progress();
                    // ||
                    return Create<LexTokenImpl<LexTokenKind::VerticalLineVerticalLineSymbol>>(
                        TextSpan(start, start + 2));
                }
                // |
                return Create<LexTokenImpl<LexTokenKind::VerticalLineSymbol>>(TextSpan(start, start + 1));
            }
            case u8'^': {
                auto n = Peek();
                if (n == u8'=') {
                    Progress();
                    // ^=
                    return Create<LexTokenImpl<LexTokenKind::CaretEqualsSymbol>>(TextSpan(start, start + 2));
                }
                if (n == u8'^') {
                    Progress();
                    // ^^
                    return Create<LexTokenImpl<LexTokenKind::CaretCaretSymbol>>(TextSpan(start, start + 2));
                }
                // ^
                return Create<LexTokenImpl<LexTokenKind::CaretSymbol>>(TextSpan(start, start + 1));
            }
            case u8'~': return Create<LexTokenImpl<LexTokenKind::TildeSymbol>>(TextSpan(start, start + 1));
            case u8'.': return Create<LexTokenImpl<LexTokenKind::DotSymbol>>(TextSpan(start, start + 1));
            case u8'[':
                return Create<LexTokenImpl<LexTokenKind::OpenBlockParenthesisSymbol>>(TextSpan(start, start + 1));
            case u8']':
                return Create<LexTokenImpl<LexTokenKind::CloseBlockParenthesisSymbol>>(TextSpan(start, start + 1));
            case u8'@': return Create<LexTokenImpl<LexTokenKind::AtSymbol>>(TextSpan(start, start + 1));

            case u8' ':
            case u8'\r':
            case u8'\n':
            case u8'\t': return Create<LexTokenImpl<LexTokenKind::Whitespace>>(TextSpan(start, start + 1));
            // Byte order mark
            case u8'\xEF': {
                if (Peek() == u8'\xBB' && Peek(2) == u8'\xBF') {
                    Progress(2);
                    return Create<LexTokenImpl<LexTokenKind::Whitespace>>(TextSpan(start, start + 3));
                }
                LogError(Diagnostics::DiagnosticType::UnknownToken, TextSpan(start, start + 1));
                return Create<LexTokenImpl<LexTokenKind::Unknown>>(TextSpan(start, start + 1));
            }
            case u8'0':
            case u8'1':
            case u8'2':
            case u8'3':
            case u8'4':
            case u8'5':
            case u8'6':
            case u8'7':
            case u8'8':
            case u8'9': return LexNumerical(c);
            case u8'\'': return LexString(u8'\'', false);
            case u8'"': {
                if (Peek() == '"' && Peek(2) == '\"') {
                    return LexString(u8'"', true);
                }
                return LexString(u8'"', false);
            }

            default:
                if (IsAlphaNumericalOrUnderscore(c))
                    return LexKeywordOrIdentifier();
                LogError(Diagnostics::DiagnosticType::UnknownToken, TextSpan(start, start + 1));
                return Create<LexTokenImpl<LexTokenKind::Unknown>>(TextSpan(start, start + 1));
        }
    }

    LexToken* Lexer::LexNumerical(char8_t c) {
        auto initialValue = LexDecimalValue(c);
        auto numericalSystem = 10; // Default to decimal system.
        if (initialValue == 0) {
            auto secondChar = Peek();
            auto secondValue = LexDecimalValue(secondChar);
            if (secondChar != '.' && secondValue == 255) {
                Progress();
                switch (secondChar) {
                    case 'x':
                    case 'X': numericalSystem = 16; break;
                    case 'd':
                    case 'D': numericalSystem = 10; break;
                    case 'o':
                    case 'O': numericalSystem = 8; break;
                    case 'b':
                    case 'B': numericalSystem = 2; break;
                    default:
                        LogError(Diagnostics::DiagnosticType::InvalidNumericalBase,
                                 TextSpan(_position - 1, _position + 1));
                        // Set to the largest numerical system, so we can prevent errors down the line.
                        numericalSystem = 16;
                        break;
                }
            }
        }
        switch (numericalSystem) {
            case 10: return LexDecimal(initialValue);
            case 16: return LexHexadecimal();
            case 8: return LexOctal();
            case 2: return LexBinary();
            default: throw std::logic_error("Not implemented");
        }
    }

    constexpr int64_t quick_pow10(int n) {
        constexpr int64_t pow10[20] = {1,
                                       10,
                                       100,
                                       1000,
                                       10000,
                                       100000,
                                       1000000,
                                       10000000,
                                       100000000,
                                       1000000000,
                                       10000000000,
                                       100000000000,
                                       1000000000000,
                                       10000000000000,
                                       10000000000000,
                                       100000000000000,
                                       1000000000000000,
                                       10000000000000000,
                                       100000000000000000,
                                       1000000000000000000};
        return pow10[n];
    }

    LexToken* Lexer::LexDecimal(ParseInt initial) {
        auto start = _position;
        ParseInt value = initial;
        ParseInt decimalValue = 0;
        ParseInt exponentValue = 0;
        uint8_t decimalLength = 0;
        bool isDecimal = false;
        bool isExponent = false;
        while (true) {
            auto v = (ParseInt)LexDecimalValue(Peek());
            if (v == 255) {
                if (!isDecimal && Peek() == u8'.') {
                    isDecimal = true;
                    Progress();
                    continue;
                }
                if (isDecimal && (Peek() == u8'e' || Peek() == u8'E')) {
                    isDecimal = false;
                    isExponent = true;
                    Progress();
                    continue;
                }
                break;
            }
            Progress();
            if (isDecimal) {
                decimalValue *= 10;
                decimalValue += v;
                decimalLength++;
            } else if (isExponent) {
                exponentValue *= 10;
                exponentValue += v;
            } else {
                value *= 10;
                value += v;
            }
        }
        if (isDecimal || isExponent) {
            auto val = value + ((ParseFloat)decimalValue / quick_pow10(decimalLength));
            if (isExponent) {
                val *= pow(10, exponentValue);
            }
            return Create<FloatLiteral>(TextSpan(start, _position), val);
        }
        return Create<IntegerLiteral>(TextSpan(start, _position), value);
    }

    IntegerLiteral* Lexer::LexHexadecimal() {
        auto start = _position;
        ParseInt value = 0;
        while (true) {
            auto v = LexHexadecimalValue(Peek());
            if (v == 255) {
                break;
            }
            Progress();
            value <<= 4;
            value += v;
        }
        return Create<IntegerLiteral>(TextSpan(start, _position), value);
    }
    IntegerLiteral* Lexer::LexOctal() {
        auto start = _position;
        ParseInt value = 0;
        while (true) {
            auto v = LexOctalValue(Peek());
            if (v == 255) {
                break;
            }
            Progress();
            value <<= 3;
            value += v;
        }
        return Create<IntegerLiteral>(TextSpan(start, _position), value);
    }
    IntegerLiteral* Lexer::LexBinary() {
        auto start = _position;
        ParseInt value = 0;
        while (true) {
            auto v = LexBinaryValue(Peek());
            if (v == 255) {
                break;
            }
            Progress();
            value <<= 1;
            value += v;
        }
        return Create<IntegerLiteral>(TextSpan(start, _position), value);
    }
    StringLiteral* Lexer::LexString(char8_t opening, bool heredoc) {
        Progress();
        if (heredoc) {
            Progress(2);
        }
        auto start = _position;
        size_t offset = 0;
        while (true) {
            auto current = Peek(offset);
            if (heredoc) {
                if (current == '"' && Peek(offset + 1) == '"' && Peek(offset + 2) == '"' && Peek(offset + 3) != '"') {
                    break;
                }
            } else if (current == opening) {
                break;
            }
            if (current == u8'\0') {
                LogError(Diagnostics::DiagnosticType::ExpectedEndOfString, TextSpan(start, start + offset));
                break;
            }
            if (!heredoc && (current == u8'\n' || current == u8'\r')) {
                LogError(Diagnostics::DiagnosticType::ExpectedEndOfString, TextSpan(start, start + offset));
                break;
            }
            offset++;
        }
        Progress(offset);
        if (heredoc) {
            Progress(2);
        }
        return Create<StringLiteral>(TextSpan(start, start + _position), ParseString(_script.substr(start, offset)));
    }

    LexToken* Lexer::LexKeywordOrIdentifier() {
        auto start = _position;
        auto offset = 0;
        while (IsAlphaNumericalOrUnderscore(Peek(offset))) {
            offset++;
        }
        auto str = _script.substr(start, offset);
        Progress(offset - 1);
        auto hash = Identifier::Hash(str);
        switch (hash) {
            case Identifier::Hash(u8"and"):
                return Create<LexTokenImpl<LexTokenKind::AndKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"abstract"):
                return Create<LexTokenImpl<LexTokenKind::AbstractKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"auto"):
                return Create<LexTokenImpl<LexTokenKind::AutoKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"bool"):
                return Create<LexTokenImpl<LexTokenKind::BoolKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"break"):
                return Create<LexTokenImpl<LexTokenKind::BreakKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"case"):
                return Create<LexTokenImpl<LexTokenKind::CaseKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"cast"):
                return Create<LexTokenImpl<LexTokenKind::CastKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"catch"):
                return Create<LexTokenImpl<LexTokenKind::CatchKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"class"):
                return Create<LexTokenImpl<LexTokenKind::ClassKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"const"):
                return Create<LexTokenImpl<LexTokenKind::ConstKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"continue"):
                return Create<LexTokenImpl<LexTokenKind::ContinueKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"default"):
                return Create<LexTokenImpl<LexTokenKind::DefaultKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"do"):
                return Create<LexTokenImpl<LexTokenKind::DoKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"double"):
                return Create<LexTokenImpl<LexTokenKind::DoubleKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"else"):
                return Create<LexTokenImpl<LexTokenKind::ElseKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"enum"):
                return Create<LexTokenImpl<LexTokenKind::EnumKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"explicit"):
                return Create<LexTokenImpl<LexTokenKind::ExplicitKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"external"):
                return Create<LexTokenImpl<LexTokenKind::ExternalKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"false"):
                return Create<LexTokenImpl<LexTokenKind::FalseKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"final"):
                return Create<LexTokenImpl<LexTokenKind::FinalKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"float"):
                return Create<LexTokenImpl<LexTokenKind::FloatKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"for"):
                return Create<LexTokenImpl<LexTokenKind::ForKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"from"):
                return Create<LexTokenImpl<LexTokenKind::FromKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"funcdef"):
                return Create<LexTokenImpl<LexTokenKind::FuncdefKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"function"):
                return Create<LexTokenImpl<LexTokenKind::FunctionKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"get"):
                return Create<LexTokenImpl<LexTokenKind::GetKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"if"):
                return Create<LexTokenImpl<LexTokenKind::IfKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"import"):
                return Create<LexTokenImpl<LexTokenKind::ImportKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"in"):
                return Create<LexTokenImpl<LexTokenKind::InKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"inout"):
                return Create<LexTokenImpl<LexTokenKind::InoutKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"int"):
                return Create<LexTokenImpl<LexTokenKind::IntKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"interface"):
                return Create<LexTokenImpl<LexTokenKind::InterfaceKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"int8"):
                return Create<LexTokenImpl<LexTokenKind::Int8Keyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"int16"):
                return Create<LexTokenImpl<LexTokenKind::Int16Keyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"int32"):
                return Create<LexTokenImpl<LexTokenKind::Int32Keyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"int64"):
                return Create<LexTokenImpl<LexTokenKind::Int64Keyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"is"):
                return Create<LexTokenImpl<LexTokenKind::IsKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"mixin"):
                return Create<LexTokenImpl<LexTokenKind::MixinKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"namespace"):
                return Create<LexTokenImpl<LexTokenKind::NamespaceKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"not"):
                return Create<LexTokenImpl<LexTokenKind::NotKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"null"):
                return Create<LexTokenImpl<LexTokenKind::NullKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"or"):
                return Create<LexTokenImpl<LexTokenKind::OrKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"out"):
                return Create<LexTokenImpl<LexTokenKind::OutKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"override"):
                return Create<LexTokenImpl<LexTokenKind::OverrideKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"private"):
                return Create<LexTokenImpl<LexTokenKind::PrivateKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"property"):
                return Create<LexTokenImpl<LexTokenKind::PropertyKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"protected"):
                return Create<LexTokenImpl<LexTokenKind::ProtectedKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"return"):
                return Create<LexTokenImpl<LexTokenKind::ReturnKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"set"):
                return Create<LexTokenImpl<LexTokenKind::SetKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"shared"):
                return Create<LexTokenImpl<LexTokenKind::SharedKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"super"):
                return Create<LexTokenImpl<LexTokenKind::SuperKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"switch"):
                return Create<LexTokenImpl<LexTokenKind::SwitchKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"this"):
                return Create<LexTokenImpl<LexTokenKind::ThisKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"true"):
                return Create<LexTokenImpl<LexTokenKind::TrueKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"try"):
                return Create<LexTokenImpl<LexTokenKind::TryKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"typedef"):
                return Create<LexTokenImpl<LexTokenKind::TypedefKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"uint"):
                return Create<LexTokenImpl<LexTokenKind::UintKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"uint8"):
                return Create<LexTokenImpl<LexTokenKind::Uint8Keyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"uint16"):
                return Create<LexTokenImpl<LexTokenKind::Uint16Keyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"uint32"):
                return Create<LexTokenImpl<LexTokenKind::Uint32Keyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"uint64"):
                return Create<LexTokenImpl<LexTokenKind::Uint64Keyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"void"):
                return Create<LexTokenImpl<LexTokenKind::VoidKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"while"):
                return Create<LexTokenImpl<LexTokenKind::WhileKeyword>>(TextSpan(start, _position));
            case Identifier::Hash(u8"xor"):
                return Create<LexTokenImpl<LexTokenKind::XorKeyword>>(TextSpan(start, _position));

            default: return Create<IdentifierToken>(TextSpan(start, _position), Identifier(str.data(), offset, hash));
        }
    }
    bool Lexer::IsAlphaNumericalOrUnderscore(char8_t c) {
        if (c >= 'a' && c <= 'z') {
            return true;
        }
        if (c >= 'A' && c <= 'Z') {
            return true;
        }
        if (c >= '0' && c <= '9') {
            return true;
        }
        if (c == '_') {
            return true;
        }
        return false;
    }
}