在解析器中考虑以下规则：
expression
: IDENTIFIER
| (...)
| procedure_call // e.g. (foo 1 2 3)
| macro_use // e.g. (xyz (some datum))
;
procedure_call
: '(' expression expression* ')'
;
macro_use
: '(' IDENTIFIER datum* ')'
;
和
// Note that any string that parses as an <expression> will also parse as a <datum>.
datum
: simple_datum
| compound_datum
;
simple_datum
: BOOLEAN
| NUMBER
| CHARACTER
| STRING
| IDENTIFIER
;
compound_datum
: list
| vector
;
list
: '(' (datum+ ( '.' datum)?)? ')'
| ABBREV_PREFIX datum
;
fragment ABBREV_PREFIX
: ('\'' | '`' | ',' | ',@')
;
vector
: '#(' datum* ')'
;
表达式规则中的procedure_call和macro_rule替代生成非LL（*）结构错误。我可以看到问题，因为(IDENTIFIER)将解析为两者。但即使我用+而不是*定义它们，它也会产生错误，即使上面的例子不应再解析了。
我提出了语法谓词的用法，但我无法弄清楚如何使用它们来做这里的技巧。
像
expression
: IDENTIFIER
| (...)
| (procedure_call)=>procedure_call // e.g. (foo 1 2 3)
| macro_use // e.g. (xyz (some datum))
;
或
expression
: IDENTIFIER
| (...)
| ('(' IDENTIFIER expression)=>procedure_call // e.g. (foo 1 2 3)
| macro_use // e.g. (xyz (some datum))
;
也不起作用，因为除了第一条规则之外的任何规则都不匹配。有没有正确的方法来解决这个问题？
答案 0 :(得分：3)
我找到了JavaCC grammar of R5RS，我曾经（很快！）编写一个等同的ANTLR：
/*
* Copyright (C) 2011 by Bart Kiers, based on the work done by Håkan L. Younes'
* JavaCC R5RS grammar, available at: http://mindprod.com/javacc/R5RS.jj
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/
grammar R5RS;
parse
: commandOrDefinition* EOF
;
commandOrDefinition
: (syntaxDefinition)=> syntaxDefinition
| (definition)=> definition
| ('(' BEGIN commandOrDefinition)=> '(' BEGIN commandOrDefinition+ ')'
| command
;
syntaxDefinition
: '(' DEFINE_SYNTAX keyword transformerSpec ')'
;
definition
: '(' DEFINE ( variable expression ')'
| '(' variable defFormals ')' body ')'
)
| '(' BEGIN definition* ')'
;
defFormals
: variable* ('.' variable)?
;
keyword
: identifier
;
transformerSpec
: '(' SYNTAX_RULES '(' identifier* ')' syntaxRule* ')'
;
syntaxRule
: '(' pattern template ')'
;
pattern
: patternIdentifier
| '(' (pattern+ ('.' pattern | ELLIPSIS)?)? ')'
| '#(' (pattern+ ELLIPSIS? )? ')'
| patternDatum
;
patternIdentifier
: syntacticKeyword
| VARIABLE
;
patternDatum
: STRING
| CHARACTER
| bool
| number
;
template
: patternIdentifier
| '(' (templateElement+ ('.' templateElement)?)? ')'
| '#(' templateElement* ')'
| templateDatum
;
templateElement
: template ELLIPSIS?
;
templateDatum
: patternDatum
;
command
: expression
;
identifier
: syntacticKeyword
| variable
;
syntacticKeyword
: expressionKeyword
| ELSE
| ARROW
| DEFINE
| UNQUOTE
| UNQUOTE_SPLICING
;
expressionKeyword
: QUOTE
| LAMBDA
| IF
| SET
| BEGIN
| COND
| AND
| OR
| CASE
| LET
| LETSTAR
| LETREC
| DO
| DELAY
| QUASIQUOTE
;
expression
: (variable)=> variable
| (literal)=> literal
| (lambdaExpression)=> lambdaExpression
| (conditional)=> conditional
| (assignment)=> assignment
| (derivedExpression)=> derivedExpression
| (procedureCall)=> procedureCall
| (macroUse)=> macroUse
| macroBlock
;
variable
: VARIABLE
| ELLIPSIS
;
literal
: quotation
| selfEvaluating
;
quotation
: '\'' datum
| '(' QUOTE datum ')'
;
selfEvaluating
: bool
| number
| CHARACTER
| STRING
;
lambdaExpression
: '(' LAMBDA formals body ')'
;
formals
: '(' (variable+ ('.' variable)?)? ')'
| variable
;
conditional
: '(' IF test consequent alternate? ')'
;
test
: expression
;
consequent
: expression
;
alternate
: expression
;
assignment
: '(' SET variable expression ')'
;
derivedExpression
: quasiquotation
| '(' ( COND ( '(' ELSE sequence ')'
| condClause+ ('(' ELSE sequence ')')?
)
| CASE expression ( '(' ELSE sequence ')'
| caseClause+ ('(' ELSE sequence ')')?
)
| AND test*
| OR test*
| LET variable? '(' bindingSpec* ')' body
| LETSTAR '(' bindingSpec* ')' body
| LETREC '(' bindingSpec* ')' body
| BEGIN sequence
| DO '(' iterationSpec* ')' '(' test doResult? ')' command*
| DELAY expression
)
')'
;
condClause
: '(' test (sequence | ARROW recipient)? ')'
;
recipient
: expression
;
caseClause
: '(' '(' datum* ')' sequence ')'
;
bindingSpec
: '(' variable expression ')'
;
iterationSpec
: '(' variable init step? ')'
;
init
: expression
;
step
: expression
;
doResult
: sequence
;
procedureCall
: '(' operator operand* ')'
;
operator
: expression
;
operand
: expression
;
macroUse
: '(' keyword datum* ')'
;
macroBlock
: '(' (LET_SYNTAX | LETREC_SYNTAX) '(' syntaxSpec* ')' body ')'
;
syntaxSpec
: '(' keyword transformerSpec ')'
;
body
: ((definition)=> definition)* sequence
;
//sequence
// : ((command)=> command)* expression
// ;
sequence
: expression+
;
datum
: simpleDatum
| compoundDatum
;
simpleDatum
: bool
| number
| CHARACTER
| STRING
| identifier
;
compoundDatum
: list
| vector
;
list
: '(' (datum+ ('.' datum)?)? ')'
| abbreviation
;
abbreviation
: abbrevPrefix datum
;
abbrevPrefix
: '\'' | '`' | ',@' | ','
;
vector
: '#(' datum* ')'
;
number
: NUM_2
| NUM_8
| NUM_10
| NUM_16
;
bool
: TRUE
| FALSE
;
quasiquotation
: quasiquotationD[1]
;
quasiquotationD[int d]
: '`' qqTemplate[d]
| '(' QUASIQUOTE qqTemplate[d] ')'
;
qqTemplate[int d]
: (expression)=> expression
| ('(' UNQUOTE)=> unquotation[d]
| simpleDatum
| vectorQQTemplate[d]
| listQQTemplate[d]
;
vectorQQTemplate[int d]
: '#(' qqTemplateOrSplice[d]* ')'
;
listQQTemplate[int d]
: '\'' qqTemplate[d]
| ('(' QUASIQUOTE)=> quasiquotationD[d+1]
| '(' (qqTemplateOrSplice[d]+ ('.' qqTemplate[d])?)? ')'
;
unquotation[int d]
: ',' qqTemplate[d-1]
| '(' UNQUOTE qqTemplate[d-1] ')'
;
qqTemplateOrSplice[int d]
: ('(' UNQUOTE_SPLICING)=> splicingUnquotation[d]
| qqTemplate[d]
;
splicingUnquotation[int d]
: ',@' qqTemplate[d-1]
| '(' UNQUOTE_SPLICING qqTemplate[d-1] ')'
;
// macro keywords
LET_SYNTAX : 'let-syntax';
LETREC_SYNTAX : 'letrec-syntax';
SYNTAX_RULES : 'syntax-rules';
DEFINE_SYNTAX : 'define-syntax';
// syntactic keywords
ELSE : 'else';
ARROW : '=>';
DEFINE : 'define';
UNQUOTE_SPLICING : 'unquote-splicing';
UNQUOTE : 'unquote';
// expression keywords
QUOTE : 'quote';
LAMBDA : 'lambda';
IF : 'if';
SET : 'set!';
BEGIN : 'begin';
COND : 'cond';
AND : 'and';
OR : 'or';
CASE : 'case';
LET : 'let';
LETSTAR : 'let*';
LETREC : 'letrec';
DO : 'do';
DELAY : 'delay';
QUASIQUOTE : 'quasiquote';
NUM_2 : PREFIX_2 COMPLEX_2;
NUM_8 : PREFIX_8 COMPLEX_8;
NUM_10 : PREFIX_10? COMPLEX_10;
NUM_16 : PREFIX_16 COMPLEX_16;
ELLIPSIS : '...';
VARIABLE
: INITIAL SUBSEQUENT*
| PECULIAR_IDENTIFIER
;
STRING : '"' STRING_ELEMENT* '"';
CHARACTER : '#\\' (~(' ' | '\n') | CHARACTER_NAME);
TRUE : '#' ('t' | 'T');
FALSE : '#' ('f' | 'F');
// to ignore
SPACE : (' ' | '\t' | '\r' | '\n') {$channel=HIDDEN;};
COMMENT : ';' ~('\r' | '\n')* {$channel=HIDDEN;};
// fragments
fragment INITIAL : LETTER | SPECIAL_INITIAL;
fragment LETTER : 'a'..'z' | 'A'..'Z';
fragment SPECIAL_INITIAL : '!' | '$' | '%' | '&' | '*' | '/' | ':' | '<' | '=' | '>' | '?' | '^' | '_' | '~';
fragment SUBSEQUENT : INITIAL | DIGIT | SPECIAL_SUBSEQUENT;
fragment DIGIT : '0'..'9';
fragment SPECIAL_SUBSEQUENT : '.' | '+' | '-' | '@';
fragment PECULIAR_IDENTIFIER : '+' | '-';
fragment STRING_ELEMENT : ~('"' | '\\') | '\\' ('"' | '\\');
fragment CHARACTER_NAME : 'space' | 'newline';
fragment COMPLEX_2
: REAL_2 ('@' REAL_2)?
| REAL_2? SIGN UREAL_2? ('i' | 'I')
;
fragment COMPLEX_8
: REAL_8 ('@' REAL_8)?
| REAL_8? SIGN UREAL_8? ('i' | 'I')
;
fragment COMPLEX_10
: REAL_10 ('@' REAL_10)?
| REAL_10? SIGN UREAL_10? ('i' | 'I')
;
fragment COMPLEX_16
: REAL_16 ('@' REAL_16)?
| REAL_16? SIGN UREAL_16? ('i' | 'I')
;
fragment REAL_2 : SIGN? UREAL_2;
fragment REAL_8 : SIGN? UREAL_8;
fragment REAL_10 : SIGN? UREAL_10;
fragment REAL_16 : SIGN? UREAL_16;
fragment UREAL_2 : UINTEGER_2 ('/' UINTEGER_2)?;
fragment UREAL_8 : UINTEGER_8 ('/' UINTEGER_8)?;
fragment UREAL_10 : UINTEGER_10 ('/' UINTEGER_10)? | DECIMAL_10;
fragment UREAL_16 : UINTEGER_16 ('/' UINTEGER_16)?;
fragment DECIMAL_10
: UINTEGER_10 SUFFIX
| '.' DIGIT+ '#'* SUFFIX?
| DIGIT+ '.' DIGIT* '#'* SUFFIX?
| DIGIT+ '#'+ '.' '#'* SUFFIX?
;
fragment UINTEGER_2 : DIGIT_2+ '#'*;
fragment UINTEGER_8 : DIGIT_8+ '#'*;
fragment UINTEGER_10 : DIGIT+ '#'*;
fragment UINTEGER_16 : DIGIT_16+ '#'*;
fragment PREFIX_2 : RADIX_2 EXACTNESS? | EXACTNESS RADIX_2;
fragment PREFIX_8 : RADIX_8 EXACTNESS? | EXACTNESS RADIX_8;
fragment PREFIX_10 : RADIX_10 EXACTNESS? | EXACTNESS RADIX_10;
fragment PREFIX_16 : RADIX_16 EXACTNESS? | EXACTNESS RADIX_16;
fragment SUFFIX : EXPONENT_MARKER SIGN? DIGIT+;
fragment EXPONENT_MARKER : 'e' | 's' | 'f' | 'd' | 'l' | 'E' | 'S' | 'F' | 'D' | 'L';
fragment SIGN : '+' | '-';
fragment EXACTNESS : '#' ('i' | 'e' | 'I' | 'E');
fragment RADIX_2 : '#' ('b' | 'B');
fragment RADIX_8 : '#' ('o' | 'O');
fragment RADIX_10 : '#' ('d' | 'D');
fragment RADIX_16 : '#' ('x' | 'X');
fragment DIGIT_2 : '0' | '1';
fragment DIGIT_8 : '0'..'7';
fragment DIGIT_16 : DIGIT | 'a'..'f' | 'A'..'F';
可以使用以下类进行测试：
import org.antlr.runtime.*;
public class Main {
public static void main(String[] args) throws Exception {
String source =
"(define sum-iter \n" +
" (lambda(n acc i) \n" +
" (if (> i n) \n" +
" acc \n" +
" (sum-iter n (+ acc i) (+ i 1))))) ";
R5RSLexer lexer = new R5RSLexer(new ANTLRStringStream(source));
R5RSParser parser = new R5RSParser(new CommonTokenStream(lexer));
parser.parse();
}
}
并生成词法分析器＆amp;解析器，编译所有Java源文件并运行主类，执行：
bart@hades:~/Programming/ANTLR/Demos/R5RS$ java -cp antlr-3.3.jar org.antlr.Tool R5RS.g bart@hades:~/Programming/ANTLR/Demos/R5RS$ javac -cp antlr-3.3.jar *.java bart@hades:~/Programming/ANTLR/Demos/R5RS$ java -cp .:antlr-3.3.jar Main bart@hades:~/Programming/ANTLR/Demos/R5RS$
控制台上没有打印任何内容的事实意味着解析器（和词法分析器）没有找到所提供源的任何错误。
请注意，我没有单元测试，只测试了Main类中的单个Scheme源。如果你在ANTLR语法中发现错误，我会很高兴听到它们，所以我可以修复语法。在适当的时候，我可能会将语法提交给官方ANTLR Wiki。