语法分析器建议 (ANTLR)

Question

好吧，我正在尝试在 Antlr4 上编写一个简单的 QBasic 语法。而 'Else-If' 循环将无法正常工作，它会在 THEN 之后自动转换为 assigncommand。你能复习一下我的语法吗，有什么改进吗？

如何用正则表达式写 string。（也用西里尔字母）

我应该写这些关键词吗('PRINT' 'IF')？或使用词法分析器（如 ..PRINTKEY; PRINTKEY : 'PRINT'）

grammar Hello3;

// AssignCommand; MainCommand; FlowCommand
prog : (assigncommand | maincommand | flowcommand)+;

// AssignInt; AssignString
// MyAge = PreviousAge + 1
// MyName$ = FirstName$ + MiddleName$ + LastName$
assigncommand : assignint | assignstring;
assignint : IDINT '=' (IDINT | INT) (OPERATORMATH (IDINT | INT))* '\n'+;
assignstring : IDSTRING '=' (IDSTRING | STRING) ('+' (IDSTRING | STRING))* '\n'+;

//PrintCommand, InputCommand
//PRINT MyName$, MyAge, "Hello", 123
//INPUT "What is your name?", yourname$
//(or)INPUT yourname$ 
maincommand : printcommand | inputcommand;
printcommand : 'PRINT' (',' (IDINT | IDSTRING | STRING | INT))+ '\n'+;
inputcommand : 'INPUT' (IDINT | IDSTRING | STRING)? ',' (IDINT | IDSTRING) '\n'+;


//If-ElseFlow; WhileFlow
//If-Else-Add; Else-Add
//
//IF a > 3 THEN
//PRINT a
//a = a -1
//ELSE IF a = 1 THEN
//b = a
//END IF
//
//WHILE a > 3
//a = a - 1
//PRINT a
//WEND
flowcommand : ifelseflow | whileflow;
ifelseflow : 'IF' conditionflow 'THEN' '\n' ifelseadd* elseadd* 'END' 'IF' '\n'+;
whileflow : 'WHILE' conditionflow '\n' (assigncommand | maincommand | flowcommand)*  'WEND' '\n'+;

conditionflow : ((INT | IDINT) OPERATORBOOL (INT | IDINT)) | ((STRING | IDSTRING) '=' (STRING | IDSTRING));
ifelseadd : 'ELSEIF' conditionflow 'THEN' '\n' ((assigncommand | maincommand | flowcommand) '\n')+;
elseadd : 'ELSE' '\n' ((assigncommand | maincommand | flowcommand) '\n')+;

//Lexers
INT : [0-9]+;
STRING : '"' [a-zA-Z\u0400-\u04FF[=10=]-9' ''?'':']+ '"'; 
IDINT : [a-zA-Z]([a-zA-Z0-9]*);       //MyAge
IDSTRING : [a-zA-Z]([a-zA-Z0-9]*)'$';  //MyName$ 
OPERATORMATH : '+'|'-'|'*'|'/';
OPERATORBOOL : '='|'>'|'<'|'>='|'<=';
WS : [ \t\r]+ -> skip;

Answer 1

像你一样，我发现用类似 BASIC 的语言实现 if..else 结构是一个真正的挑战。我在网上找到了一些很好的资源。请看看我的语法片段：

ifstmt
:   IF condition_block (ELSE IF condition_block)* (ELSE stmt_block)?
;

condition_block
:   expr stmt_block
;

stmt_block
:   OBRACE statement+ CBRACE
|   statement
;

我的实现（在 C# 访问者模式中）：

    public override MuValue VisitIfstmt(LISBASICParser.IfstmtContext context)
    {
        LISBASICParser.Condition_blockContext[] conditions = context.condition_block();
        bool evaluatedBlock = false;
        foreach (LISBASICParser.Condition_blockContext condition in conditions)
        {
            MuValue evaluated = Visit(condition.expr());
            if (evaluated.AsBoolean())
            {
                evaluatedBlock = true;
                Visit(condition.stmt_block());
                break;
            }
        }
        if (!evaluatedBlock && context.stmt_block() != null)
        {
            Visit(context.stmt_block());
        }
        return MuValue.Void;
    }

我从 Bart Kiers 对他的 Mu 语言的出色实现中借鉴了 MuValue 的想法。他的那个项目中有很多很棒的想法。

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