有没有好心人帮忙 review 一下， Java 数字的词法解析实现

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这是一个创建于 596 天前的主题，其中的信息可能已经有所发展或是发生改变。

代码如下

其他的部分还没有完成，只考虑数值解析这一段。主要是从可读性跟性能两个方面看

package compile.craft;

import lombok.extern.slf4j.Slf4j;

import static compile.craft.CharUtils.*;

@Slf4j
public class Lexer {

    boolean fetchedEOF = false;

    private final String source;
    private int pos = 0;
    private char ch;
    private int line = 0;
    private int col = 0;

    public Lexer(String source) {
        this.source = source;
    }

    /**
     * 1. line 维护
     *
     */
    public Token nextToken() {
        if (fetchedEOF) {
            return null;
        }

        while (true) {
            do {
                advance();
            } while (isBlank(ch));

            if (ch == EOF) {
                fetchedEOF = true;
                return null;
            }

            // 处理 // 注释

            if (isIdentifierStart(ch)) {
                return scanIdentifier();
            }

            if (ch == '.') {
                return scanNumber();
            }

            if (CharUtils.isDigit(ch)) {
                return scanNumber();
            }

            break;
        }

        return null;
    }

    private Token scanNumber() {
        int start = pos - 1;
        TokenKind tokenKind = null;

        if (ch == '0') {
            advance();

            // HEX_LITERAL:        '0' [xX] [0-9a-fA-F] ([0-9a-fA-F_]* [0-9a-fA-F])? [lL]?;
            // HEX_FLOAT_LITERAL:  '0' [xX] (HexDigits '.'? | HexDigits? '.' HexDigits) [pP] [+-]? Digits [fFdD]?;
            // HexDigits: HexDigit ((HexDigit | '_')* HexDigit)?;
            // Digits: [0-9] ([0-9_]* [0-9])?;

            if (ch == 'x' || ch == 'X') {
                if (peek() == '.') {
                    advance();
                    scanHexFraction(false);
                    String lexeme = source.substring(start, pos);
                    return new Token(TokenKind.HEX_FLOAT_LITERAL, lexeme);
                } else {
                    scanHex();

                    if (ch == '.') {
                        scanHexFraction(true);
                        tokenKind = TokenKind.HEX_FLOAT_LITERAL;
                    } else if (ch == 'p' || ch == 'P') {
                        scanExp();
                        tokenKind = TokenKind.HEX_FLOAT_LITERAL;
                    } else if (ch == 'f' || ch == 'F' || ch == 'd' || ch == 'D') {
                        tokenKind = TokenKind.HEX_FLOAT_LITERAL;
                    } else if (ch == 'l' || ch == 'L') {
                        tokenKind = TokenKind.HEX_LITERAL;
                    } else {
                        retreat();
                        tokenKind = TokenKind.HEX_LITERAL;
                    }

                    String lexeme = source.substring(start, pos);
                    return new Token(tokenKind, lexeme);
                }
            } else if (ch == 'b' || ch == 'B') {
                // BINARY_LITERAL:     '0' [bB] [01] ([01_]* [01])? [lL]?;
                scanBit();

                if ((ch != 'l') && (ch != 'L')) {
                    retreat();
                }

                String lexeme = source.substring(start, pos);
                return new Token(TokenKind.BINARY_LITERAL, lexeme);
            } else if (ch == '_' || isOct(ch)) {
                // OCT_LITERAL:        '0' '_'* [0-7] ([0-7_]* [0-7])? [lL]?;
                // FLOAT_LITERAL:      (Digits '.' Digits? | '.' Digits) ExponentPart? [fFdD]?;
                // FLOAT_LITERAL:      Digits (ExponentPart [fFdD]? | [fFdD]);
                scanOct();

                if (isDigit(ch)) {
                    scanDigit();

                    if (ch == '.') {
                        scanFraction();
                    } else if (ch == 'e' || ch == 'E') {
                        scanExp();
                    } else if ((ch != 'f') && (ch != 'F') && (ch != 'd') && (ch != 'D')) {
                        error("invalid oct literal");
                    }

                    tokenKind = TokenKind.FLOAT_LITERAL;
                } else if (ch == '.') {
                    scanFraction();
                    tokenKind = TokenKind.FLOAT_LITERAL;
                } else if (ch == 'e' || ch == 'E') {
                    scanExp();
                    tokenKind = TokenKind.FLOAT_LITERAL;
                } else if (ch == 'd' || ch == 'D' || ch == 'f' || ch == 'F') {
                    tokenKind = TokenKind.FLOAT_LITERAL;
                } else if (ch == 'l' || ch == 'L') {
                    tokenKind = TokenKind.OCT_LITERAL;
                } else {
                    retreat();
                    tokenKind = TokenKind.OCT_LITERAL;
                }

                String lexeme = source.substring(start, pos);
                return new Token(tokenKind, lexeme);
            } else {
                // FLOAT_LITERAL:      (Digits '.' Digits? | '.' Digits) ExponentPart? [fFdD]?;
                // FLOAT_LITERAL:      Digits (ExponentPart [fFdD]? | [fFdD]);
                // DECIMAL_LITERAL:    ('0' | [1-9] (Digits? | '_'+ Digits)) [lL]?;
                // ExponentPart:       [eE] [+-]? Digits;

                if (isDigit(ch)) {
                    do {
                        advance();
                    } while (isDigit(ch));

                    if (ch == '.') {
                        scanFraction();
                        tokenKind = TokenKind.FLOAT_LITERAL;
                    } else if (ch == 'e' || ch == 'E') {
                        scanExp();
                        tokenKind = TokenKind.FLOAT_LITERAL;
                    } else if ((ch == 'f') || ch == 'F' || ch == 'd' || ch == 'D') {
                        tokenKind = TokenKind.FLOAT_LITERAL;
                    } else {
                        error("invalid float literal");
                    }
                } else if (ch == '.') {
                    scanFraction();
                    tokenKind = TokenKind.FLOAT_LITERAL;
                } else if (ch == 'e' || ch == 'E') {
                    scanExp();
                    tokenKind = TokenKind.FLOAT_LITERAL;
                } else if (ch == 'l' || ch == 'L') {
                    tokenKind = TokenKind.DECIMAL_LITERAL;
                } else if (ch == 'f' || ch == 'F' || ch == 'd' || ch == 'D') {
                    tokenKind = TokenKind.FLOAT_LITERAL;
                } else {
                    retreat();
                    tokenKind = TokenKind.DECIMAL_LITERAL;
                }

                String lexeme = source.substring(start, pos);
                return new Token(tokenKind, lexeme);
            }
        } else {
            // FLOAT_LITERAL:      (Digits '.' Digits? | '.' Digits) ExponentPart? [fFdD]?;
            // FLOAT_LITERAL:      Digits (ExponentPart [fFdD]? | [fFdD]);
            // DECIMAL_LITERAL:    ('0' | [1-9] (Digits? | '_'+ Digits)) [lL]?;
            // ExponentPart:       [eE] [+-]? Digits;
            if (ch == '.') {
                scanDigit();

                if (ch == 'e' || ch == 'E') {
                    scanExp();
                }

                tokenKind = TokenKind.FLOAT_LITERAL;
            } else {
                scanDigit(true);

                if (ch == '.') {
                    scanFraction();
                    tokenKind = TokenKind.FLOAT_LITERAL;
                } else if (ch == 'e' || ch == 'E') {
                    scanExp();
                    tokenKind = TokenKind.FLOAT_LITERAL;
                } else if (ch == 'f' || ch == 'F' || ch == 'd' || ch == 'D') {
                    tokenKind = TokenKind.FLOAT_LITERAL;
                } else if (ch == 'l' || ch == 'L') {
                    tokenKind = TokenKind.DECIMAL_LITERAL;
                } else {
                    retreat();
                    tokenKind = TokenKind.DECIMAL_LITERAL;
                }
            }

            String lexeme = source.substring(start, pos);
            return new Token(tokenKind, lexeme);
        }
    }

    private Token scanIdentifier() {
        int start = pos - 1;

        do {
            advance();
        } while (isIdentifierChar(ch));

        String lexeme = source.substring(start, pos);
        retreat();

        if (Token.isKeyword(lexeme)) {
            TokenKind kind = Token.kind(lexeme);
            return new Token(kind, kind.literal);
        } else {
            return new Token(TokenKind.IDENTIFIER, lexeme);
        }
    }

    private void scanHex() {
        advance();

        if (!isHex(ch)) {
            error("invalid hexadecimal literal");
        }

        do {
            if (ch == '_') {
                do {
                    advance();
                } while(ch == '_');

                if (!isHex(ch)) {
                    error("invalid hexadecimal literal");
                }
            }

            do {
                advance();
            } while (isHex(ch));
        } while (ch == '_');
    }

    private void scanBit() {
        advance();

        if (!isBit(ch)) {
            error("invalid binary literal");
        }

        do {
            if (ch == '_') {
                do {
                    advance();
                } while(ch == '_');

                if (!isBit(ch)) {
                    error("invalid binary literal");
                }
            }

            do {
                advance();
            } while (isBit(ch));
        } while (ch == '_');
    }

    private void scanOct() {
        do {
            if (ch == '_') {
                do {
                    advance();
                } while(ch == '_');

                if (!isDigit(ch)) {
                    error("invalid octal literal");
                }

                if (!isOct(ch)) {
                    return;
                }
            }

            do {
                advance();
            } while (isOct(ch));
        } while (ch == '_');
    }

    private void scanDigit(boolean hasDigit) {
        advance();

        if (hasDigit) {
            if ((ch != '_') && !isDigit(ch)) {
                return;
            }
        } else if (!isDigit(ch)) {
            error("invalid decimal literal");
        }

        do {
            if (ch == '_') {
                do {
                    advance();
                } while(ch == '_');

                if (!isDigit(ch)) {
                    error("invalid decimal literal");
                }
            }

            do {
                advance();
            } while (isDigit(ch));
        } while (ch == '_');
    }

    private void scanDigit() {
        scanDigit(false);
    }

    // FLOAT_LITERAL:      (Digits '.' Digits? | '.' Digits) ExponentPart? [fFdD]?;
    private void scanFraction() {
        if (isDigit(peek())) {
            scanDigit();
        } else {
            advance();
        }

        if (ch == 'e' || ch == 'E') {
            char c = peek();

            if (c == '+' || c == '-') {
                advance();
            }

            scanDigit();
        }

        if ((ch != 'f') && (ch != 'F') && (ch != 'd') && (ch != 'D')) {
            retreat();
        }
    }

    // HEX_FLOAT_LITERAL:  '0' [xX] (HexDigits '.'? | HexDigits? '.' HexDigits) [pP] [+-]? Digits [fFdD]?;
    private void scanHexFraction(boolean hasDigit) {
        if (hasDigit) {
            if (isHex(peek())) {
                scanHex();
            } else {
                advance();
            }
        } else {
            scanHex();
        }

        if ((ch != 'p') && (ch != 'P')) {
            error("invalid hexadecimal literal");
        }

        char c = peek();

        if (c == '+' || c == '-') {
            advance();
        }

        scanDigit();

        if ((ch != 'f') && (ch != 'F') && (ch != 'd') && (ch != 'D')) {
            retreat();
        }
    }

    private void scanExp() {
        char c = peek();

        if (c == '+' || c == '-') {
            advance();
        }

        scanDigit();

        if ((ch != 'f') && (ch != 'F') && (ch != 'd') && (ch != 'D')) {
            retreat();
        }
    }

    private void advance() {
        if (pos >= source.length()) {
            ch = CharUtils.EOF;
            return;
        }

        ch = source.charAt(pos++);
    }

    private void retreat() {
        if (ch != EOF) {
            if (--pos < 0) {
                error("tokenizer exceed beginning of source");
            }
        }
    }

    private char peek() {
        if (pos >= source.length()) {
            return EOF;
        }

        return source.charAt(pos);
    }

    private void error(String msg) {
        log.error("lexer error: {}", msg);
        throw new RuntimeException(msg);
    }
}

11 条回复 • 2023-03-31 14:45:58 +08:00

angryPHP

2023-03-30 19:48:57 +08:00

有没有测试用例啊

lucaslee

2023-03-30 21:56:35 +08:00

第一印象：满屏的 edfl 字符判断都看晕了 XD

kwh

2023-03-30 22:03:06 +08:00

chatGPT：让我试试

neptuno

2023-03-30 22:08:42 +08:00 via iPhone

好长

NeoZephyr

2023-03-30 22:11:37 +08:00

@angryPHP

有的

```java
def "scan number without exception"() {
when:
Lexer lexer = new Lexer(source)
Token token = lexer.nextToken()

then:
kind == token.kind.name()
lexeme == token.lexeme

where:
source | kind | lexeme

// BINARY_LITERAL: '0' [bB] [01] ([01_]* [01])? [lL]?;
"0b0" | "BINARY_LITERAL" | "0b0"
"0b1" | "BINARY_LITERAL" | "0b1"
"0b000" | "BINARY_LITERAL" | "0b000"
"0b010" | "BINARY_LITERAL" | "0b010"
"0B0L" | "BINARY_LITERAL" | "0B0L"
"0b10___10l" | "BINARY_LITERAL" | "0b10___10l"
"0b000___0L" | "BINARY_LITERAL" | "0b000___0L"
"0b001___0L" | "BINARY_LITERAL" | "0b001___0L"

// OCT_LITERAL: '0' '_'* [0-7] ([0-7_]* [0-7])? [lL]?;

"0000" | "OCT_LITERAL" | "0000"
"0__007_2" | "OCT_LITERAL" | "0__007_2"
"0__7_0L" | "OCT_LITERAL" | "0__7_0L"
"07_0L" | "OCT_LITERAL" | "07_0L"
"0000l" | "OCT_LITERAL" | "0000l"
"0007l" | "OCT_LITERAL" | "0007l"
"0_00_77__0L" | "OCT_LITERAL" | "0_00_77__0L"

// HEX_LITERAL: '0' [xX] [0-9a-fA-F] ([0-9a-fA-F_]* [0-9a-fA-F])? [lL]?;

"0x0" | "HEX_LITERAL" | "0x0"
"0x000l" | "HEX_LITERAL" | "0x000l"
"0x0eeeL" | "HEX_LITERAL" | "0x0eeeL"
"0x000eee" | "HEX_LITERAL" | "0x000eee"
"0x1_E2E3e5" | "HEX_LITERAL" | "0x1_E2E3e5"
"0xe___ee_eL" | "HEX_LITERAL" | "0xe___ee_eL"

// DECIMAL_LITERAL: ('0' | [1-9] (Digits? | '_'+ Digits)) [lL]?;

"0L" | "DECIMAL_LITERAL" | "0L"
"0" | "DECIMAL_LITERAL" | "0"
"9l" | "DECIMAL_LITERAL" | "9l"
"99___9L" | "DECIMAL_LITERAL" | "99___9L"
"9___99___9L" | "DECIMAL_LITERAL" | "9___99___9L"
"9999" | "DECIMAL_LITERAL" | "9999"
"1_000_000" | "DECIMAL_LITERAL" | "1_000_000"

// HEX_FLOAT_LITERAL: '0' [xX] (HexDigits '.'? | HexDigits? '.' HexDigits) [pP] [+-]? Digits [fFdD]?;

"0x.fp012" | "HEX_FLOAT_LITERAL" | "0x.fp012"
"0x.f__f_fp-0012d" | "HEX_FLOAT_LITERAL" | "0x.f__f_fp-0012d"
"0xf_ffP12d" | "HEX_FLOAT_LITERAL" | "0xf_ffP12d"
"0xf_f.P-12d" | "HEX_FLOAT_LITERAL" | "0xf_f.P-12d"
"0xf_f.f_fP+12" | "HEX_FLOAT_LITERAL" | "0xf_f.f_fP+12"
"0x0.0000000fp-11" | "HEX_FLOAT_LITERAL" | "0x0.0000000fp-11"
"0xf_ff.P12d" | "HEX_FLOAT_LITERAL" | "0xf_ff.P12d"
"0X0P0f" | "HEX_FLOAT_LITERAL" | "0X0P0f"
"0X0P0" | "HEX_FLOAT_LITERAL" | "0X0P0"
"0X0_0__123P0f" | "HEX_FLOAT_LITERAL" | "0X0_0__123P0f"
"0XeP0f" | "HEX_FLOAT_LITERAL" | "0XeP0f"
"0X000.P0f" | "HEX_FLOAT_LITERAL" | "0X000.P0f"
"0X00e.P0f" | "HEX_FLOAT_LITERAL" | "0X00e.P0f"
"0X0e__0.0P0f" | "HEX_FLOAT_LITERAL" | "0X0e__0.0P0f"
"0X0e__0.0__0P0f" | "HEX_FLOAT_LITERAL" | "0X0e__0.0__0P0f"
"0X0e__0.0__e0P-0__0f" | "HEX_FLOAT_LITERAL" | "0X0e__0.0__e0P-0__0f"
"0X0e__0.0__e0P+0_1__0f" | "HEX_FLOAT_LITERAL" | "0X0e__0.0__e0P+0_1__0f"
"0X0.0__e0P+0_1__0f" | "HEX_FLOAT_LITERAL" | "0X0.0__e0P+0_1__0f"
"0X0.00P0f" | "HEX_FLOAT_LITERAL" | "0X0.00P0f"
"0X0.0eP0f" | "HEX_FLOAT_LITERAL" | "0X0.0eP0f"
"0X0.e__00P0f" | "HEX_FLOAT_LITERAL" | "0X0.e__00P0f"
"0X0.e__00__0P0f" | "HEX_FLOAT_LITERAL" | "0X0.e__00__0P0f"
"0X0.e__00__e0P-0__0f" | "HEX_FLOAT_LITERAL" | "0X0.e__00__e0P-0__0f"
"0X0e.0__00__e0P+0_1__0f" | "HEX_FLOAT_LITERAL" | "0X0e.0__00__e0P+0_1__0f"
"0X.0__00__e0P-0_1__0F" | "HEX_FLOAT_LITERAL" | "0X.0__00__e0P-0_1__0F"
"0X.0__00__e0P-0_1__0" | "HEX_FLOAT_LITERAL" | "0X.0__00__e0P-0_1__0"

// FLOAT_LITERAL: (Digits '.' Digits? | '.' Digits) ExponentPart? [fFdD]?;
// FLOAT_LITERAL: Digits (ExponentPart [fFdD]? | [fFdD]);
// ExponentPart: [eE] [+-]? Digits

"0f" | "FLOAT_LITERAL" | "0f"
"00f" | "FLOAT_LITERAL" | "00f"
"0__0_0f" | "FLOAT_LITERAL" | "0__0_0f"
"0001f" | "FLOAT_LITERAL" | "0001f"
"0e0f" | "FLOAT_LITERAL" | "0e0f"
"0e0" | "FLOAT_LITERAL" | "0e0"
"1e1" | "FLOAT_LITERAL" | "1e1"
"0_0e-0_0f" | "FLOAT_LITERAL" | "0_0e-0_0f"
"0_0e0_120f" | "FLOAT_LITERAL" | "0_0e0_120f"
"0001e0009" | "FLOAT_LITERAL" | "0001e0009"
"000012345e1" | "FLOAT_LITERAL" | "000012345e1"
"0_00___9900d" | "FLOAT_LITERAL" | "0_00___9900d"
".0" | "FLOAT_LITERAL" | ".0"
".0e0" | "FLOAT_LITERAL" | ".0e0"
".0_000" | "FLOAT_LITERAL" | ".0_000"
".0___0990" | "FLOAT_LITERAL" | ".0___0990"
".000e0__0__0" | "FLOAT_LITERAL" | ".000e0__0__0"
".000e0__0__0f" | "FLOAT_LITERAL" | ".000e0__0__0f"
".000e-0__9__0f" | "FLOAT_LITERAL" | ".000e-0__9__0f"
".9e-0__1_0f" | "FLOAT_LITERAL" | ".9e-0__1_0f"
"0__00." | "FLOAT_LITERAL" | "0__00."
"0__090." | "FLOAT_LITERAL" | "0__090."
"99__9." | "FLOAT_LITERAL" | "99__9."
"000.000" | "FLOAT_LITERAL" | "000.000"
"0__10.090" | "FLOAT_LITERAL" | "0__10.090"
"000__1_0.090" | "FLOAT_LITERAL" | "000__1_0.090"
"000__1_0.090e12" | "FLOAT_LITERAL" | "000__1_0.090e12"
"0__10.090e1__00" | "FLOAT_LITERAL" | "0__10.090e1__00"
"3.1415926" | "FLOAT_LITERAL" | "3.1415926"
"0.030" | "FLOAT_LITERAL" | "0.030"
"0.6" | "FLOAT_LITERAL" | "0.6"
".0f" | "FLOAT_LITERAL" | ".0f"
".0_000f" | "FLOAT_LITERAL" | ".0_000f"
".0___0990f" | "FLOAT_LITERAL" | ".0___0990f"
".000e0__0__0f" | "FLOAT_LITERAL" | ".000e0__0__0f"
"0__00.f" | "FLOAT_LITERAL" | "0__00.f"
"0__090.f" | "FLOAT_LITERAL" | "0__090.f"
"99__9.f" | "FLOAT_LITERAL" | "99__9.f"
"000.000f" | "FLOAT_LITERAL" | "000.000f"
"0__10.090f" | "FLOAT_LITERAL" | "0__10.090f"
"000__1_0.090f" | "FLOAT_LITERAL" | "000__1_0.090f"
"000__1_0.090e12f" | "FLOAT_LITERAL" | "000__1_0.090e12f"
"0__10.090e1__00f" | "FLOAT_LITERAL" | "0__10.090e1__00f"
"3.1415926f" | "FLOAT_LITERAL" | "3.1415926f"
"0.030f" | "FLOAT_LITERAL" | "0.030f"
"0.6f" | "FLOAT_LITERAL" | "0.6f"
}
```

NeoZephyr

2023-03-30 22:12:17 +08:00

@kwh 我问了，他给的建议，感觉不大实用

NeoZephyr

2023-03-30 22:12:47 +08:00

@lucaslee

手写的，我也没有想到比较好的办法

lucaslee

2023-03-30 22:50:48 +08:00

才看到注释，写那么多代码是在翻译正则？

Leviathann

2023-03-30 23:02:58 +08:00

见不得这种副作用满天飞的代码

popvlovs

2023-03-31 13:56:52 +08:00

看的我眼花 o_o ....
我只用过 antlr ，从来没考虑过自己手搓 lexer ，这是要拿来练手么？

NeoZephyr

2023-03-31 14:45:58 +08:00

@popvlovs

我也想知道不用 antlr 这种工具，有啥比较好的办法实现 lexer