是的,你是对的:这是通过多次 AST 完成的。
首先创建一个语法来构建源的 AST,然后创建一个树语法,用于迭代树并发现所有定义的函数。然后,您可以使用另一个树语法来评估脚本,该语法从先前的树语法中获取发现的函数。
A demo.
取源码:
<?php
f(); // function called before it’s defined
function f() {
g();
}
function g() {}
?>
它被解析为以下 AST:
使用(组合)语法:
grammar PHPMin;
options {
output=AST;
}
tokens {
SCRIPT; F_CALL; F_DECL; F_BODY;
}
parse
: script EOF -> script
;
script
: '<?php' atom* '?>' -> ^(SCRIPT atom*)
;
atom
: functionCall
| functionDecl
;
functionCall
: Identifier '(' ')' ';' -> ^(F_CALL Identifier)
;
functionDecl
: 'function' Identifier '(' ')' '{' functionBody '}' -> ^(F_DECL Identifier functionBody)
;
functionBody
: functionCall* -> ^(F_BODY functionCall*)
;
Identifier : ('a'..'z' | 'A'..'Z' | '_') ('a'..'z' | 'A'..'Z' | '_' | '0'..'9')* ;
LineComment : '//' ~('\r' | '\n')* ('\r'? '\n' | EOF){skip();} ;
Space : (' ' | '\t' | '\r' | '\n'){skip();} ;
然后使用从以下树语法生成的“tree-walker”发现声明的函数:
tree grammar PHPMinFunctionWalker;
options {
tokenVocab=PHPMin;
ASTLabelType=CommonTree;
}
@members {
java.util.Set<String> declared = new java.util.HashSet<String>();
}
discover
: script
;
script
: ^(SCRIPT atom*)
;
atom
: functionCall
| functionDecl
;
functionCall
: ^(F_CALL Identifier)
;
functionDecl
: ^(F_DECL Identifier functionBody) {declared.add($Identifier.text);}
;
functionBody
: ^(F_BODY functionCall*)
;
为了测试这一切,创建一个词法分析器和解析器 (A),生成“tree-walker”(B),编译所有源文件 (C):
// A
java -cp antlr-3.2.jar org.antlr.Tool PHPMin.g
// B
java -cp antlr-3.2.jar org.antlr.Tool PHPMinFunctionWalker.g
// C
javac -cp antlr-3.2.jar *.java
// D
java -cp .:antlr-3.2.jar Main // *nix
java -cp .;antlr-3.2.jar Main // Windows
并运行以下主类(D):
import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;
import org.antlr.stringtemplate.*;
public class Main {
public static void main(String[] args) throws Exception {
String source = "<?php \n" +
"f(); // function called before it’s defined \n" +
"function f() { \n" +
" g(); \n" +
"} \n" +
"function g() {} \n" +
"?> \n";
// create a lexer and parser for the source
ANTLRStringStream in = new ANTLRStringStream(source);
PHPMinLexer lexer = new PHPMinLexer(in);
CommonTokenStream tokens = new CommonTokenStream(lexer);
PHPMinParser parser = new PHPMinParser(tokens);
PHPMinParser.parse_return returnValue = parser.parse();
CommonTree tree = (CommonTree)returnValue.getTree();
// create a tree walker to discover all declared functions
CommonTreeNodeStream nodes = new CommonTreeNodeStream(tree);
nodes.setTokenStream(tokens);
PHPMinFunctionWalker functions = new PHPMinFunctionWalker(nodes);
functions.discover();
System.out.println("Declared functions: "+functions.declared);
}
}
产生以下输出:
Declared functions: [f, g]
当然,这只是如何实现它的一个示例,而不是如何最好地完成它的示例。我可以想象(当使用 Java 解释脚本时),您不会将声明的函数作为简单的字符串存储在Set<String>
,而是作为Map<String, CommonTree>
轻松获取函数的根并在调用时对其求值。
进一步阅读:http://www.antlr.org/wiki/display/ANTLR3/Simple+tree-based+interpeter http://www.antlr.org/wiki/display/ANTLR3/Simple+tree-based+interpeter
祝你好运!
EDIT
然后,秒数传递可以检查是否使用之前的树遍历器在其之前定义了所有函数:
tree grammar PHPMinValidateWalker;
options {
tokenVocab=PHPMin;
ASTLabelType=CommonTree;
}
@members {
java.util.Set<String> declared = new java.util.HashSet<String>();
}
validate
: script
;
script
: ^(SCRIPT atom*)
;
atom
: functionCall
| functionDecl
;
functionCall
: ^(F_CALL Identifier)
{
if(!declared.contains($Identifier.text)) {
throw new RuntimeException("no such function: " + $Identifier.text);
}
}
;
functionDecl
: ^(F_DECL Identifier functionBody)
;
functionBody
: ^(F_BODY functionCall*)
;
使用测试:
import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;
import org.antlr.stringtemplate.*;
public class Main {
public static void main(String[] args) throws Exception {
String source = "<?php \n" +
"f(); // function called before it’s defined \n" +
"function f() { \n" +
" g(); \n" +
" x(); \n" +
"} \n" +
"function g() {} \n" +
"?> \n";
// create a lexer and parser for the source
ANTLRStringStream in = new ANTLRStringStream(source);
PHPMinLexer lexer = new PHPMinLexer(in);
CommonTokenStream tokens = new CommonTokenStream(lexer);
PHPMinParser parser = new PHPMinParser(tokens);
PHPMinParser.parse_return returnValue = parser.parse();
CommonTree tree = (CommonTree)returnValue.getTree();
// create a tree walker to discover all declared functions
CommonTreeNodeStream nodes = new CommonTreeNodeStream(tree);
nodes.setTokenStream(tokens);
PHPMinFunctionWalker functions = new PHPMinFunctionWalker(nodes);
functions.discover();
System.out.println("Declared functions: "+functions.declared);
// PHPMinValidateWalker
nodes = new CommonTreeNodeStream(tree);
nodes.setTokenStream(tokens);
PHPMinValidateWalker validator = new PHPMinValidateWalker(nodes);
validator.declared = functions.declared;
validator.validate();
}
}
产生异常,因为x()
没有在任何地方定义。从源中删除它将导致树遍历器不会产生异常。