I am trying to implement a translator using ANTLR+StringTemplate. I have a starting language that is java like and multiple destination language.
I used the example: http://www.antlr.org/wiki/display/ST/Language+Translation+Using+ANTLR+and+StringTemplate
One of my destination language needs all variables to be declared globally. I wrote a grammar that recognizes variables, but i cannot find e way in my template for making a local variable to be declared globally.
Of course if I would have just one translation I would be able to do it, but I have multiple translation and some of them have local and global variables. I'd like to make it in the specific template file.
For example it would be great if I could define some sort of variables inside the template for keeping a list of all variable declarations and use it at the end when i define the global scope... but i don't know if this is possibile.
The parser will have to track the variables before passing them to a template. This doesn't mean that you need one parser for a global-based target and another for the other targets, it just means that you need to define some empty templates in the targets.
Here is a very simple example of how this can be done. I don't propose that your case is this ideal, but I hope it gives you enough to work with.
Assume that your source grammar, the Java-like one, accepts code like this:
class Foobar {
var a;
var b;
var myMethod(var x, var y) {
var c;
var d;
}
}
Class Foobar contains member fields a and b, and member method myMethod contains locals c and d. For argument's sake, assume that you want a, b, c, and d to be treated as global variables for a global target, and like normal variables otherwise.
Here is a grammar that accepts the input defined above, prepped for template output:
grammar JavaLikeToTemplate;
options {
output = template;
}
@members {
private java.util.ArrayList<String> globals = new java.util.ArrayList<String>();
}
compilationUnit : class_def EOF
-> compilationUnit(classDef={$class_def.st}, globals={globals});
class_def : CLASS ID LCUR class_body RCUR
-> class(name={$ID.text}, body={$class_body.st});
class_body : (t+=class_element)+
-> append(parts={$t});
class_element : class_field
-> {$class_field.st}
| class_method
-> {$class_method.st};
class_field : VAR ID SEMI {globals.add($ID.text);}
-> classField(name={$ID.text});
class_method : VAR ID LPAR paramlist? RPAR LCUR method_body RCUR
-> classMethod(name={$ID.text}, params={$paramlist.st}, body={$method_body.st});
method_body : (t+=method_element)+
-> append(parts={$t});
method_element : method_field
-> {$method_field.st};
method_field : VAR ID SEMI {globals.add($ID.text);}
-> methodField(name={$ID.text});
paramlist : VAR t+=ID (COMMA VAR t+=ID)*
-> paramList(params={$t});
CLASS : 'class';
VAR : 'var';
ID : ('a'..'z'|'A'..'Z')('a'..'z'|'A'..'Z'|'_'|'0'..'9')*;
INT : ('0'..'9')+;
COMMA : ',';
SEMI : ';';
LCUR : '{';
RCUR : '}';
LPAR : '(';
RPAR : ')';
EQ : '=';
WS : (' '|'\t'|'\f'|'\r'|'\n'){skip();};
Note that parser member globals tracks the names of variables that a globals-only target is concerned about, but that templates pertaining to fields/variables are still called. This ensures that the grammar is target-neutral.
Here is a template that produces Java code. Note that compilationUnit ignores input globals because Java doesn't use them.
group JavaLikeToJava;
compilationUnit(globals, classDef) ::=
<<
<classDef>
>>
class(name, body) ::=
<<
public class <name> {
<body>
}
>>
classField(name) ::=
<<
private Object <name>;
>>
classMethod(name, params, body) ::=
<<
public Object <name>(<params>) {
<body>
}
>>
methodField(name) ::=
<<
Object <name>;
>>
paramList(params) ::=
<<
<params:{p|Object <p.text>}; separator=", ">
>>
append(parts) ::=
<<
<parts;separator="\n">
>>
Here is a template for a globals target. Note that many of the class templates are empty, but that compilationUnit processes input globals.
group JavaLikeToGlobal;
globals(names) ::=
<<
<names:global()>
>>
global(name) ::=
<<
global <name>
>>
compilationUnit(globals, classDef) ::=
<<
<globals:globals();separator="\n">
<classDef>
>>
class(name, body) ::=
<<
<body>
>>
classField(name) ::=
<<>>
classMethod(name, params, body) ::=
<<
<name>(<params>):
<body>
end
>>
methodField(name) ::=
<<
>>
paramList(params) ::=
<<
<params:{p| <p.text>}; separator=", ">
>>
append(parts) ::=
<<
<parts;separator="\n">
>>
Here is the launcher class I'll use to test the grammar and templates.
public class JavaLikeToTemplateTest {
public static void main(String[] args) throws Exception {
final String code = "class Foobar {\n var Foobar_a;\n var Foobar_b;\n var doSomething() {\n var doSomething_a;\n var doSomething_b;\n }\n}";
process(code, "JavaLikeToJava.stg");
process(code, "JavaLikeToGlobal.stg");
}
private static void process(final String code, String templateResourceName)
throws IOException, RecognitionException, Exception {
CharStream input = new ANTLRStringStream(code);
JavaLikeToTemplateLexer lexer = new JavaLikeToTemplateLexer(input);
CommonTokenStream tokens = new CommonTokenStream(lexer);
JavaLikeToTemplateParser parser = new JavaLikeToTemplateParser(tokens);
InputStream stream = JavaLikeToTemplateTest.class.getResourceAsStream(templateResourceName);
Reader reader = new InputStreamReader(stream);
parser.setTemplateLib(new StringTemplateGroup(reader));
reader.close();
stream.close();
JavaLikeToTemplateParser.compilationUnit_return result = parser.compilationUnit();
if (parser.getNumberOfSyntaxErrors() > 0){
throw new Exception("Syntax Errors encountered!");
}
System.out.printf("Result with %s:%n%n", templateResourceName);
System.out.println(result.toString());
}
}
Here is the input hard-coded in the test class:
class Foobar {
var Foobar_a;
var Foobar_b;
var doSomething() {
var doSomething_a;
var doSomething_b;
}
}
And here is the output produced by the code, using both templates:
Result with JavaLikeToJava.stg:
public class Foobar {
private Object Foobar_a;
private Object Foobar_b;
public Object doSomething() {
Object doSomething_a;
Object doSomething_b;
}
}
Result with JavaLikeToGlobal.stg:
global Foobar_a
global Foobar_b
global doSomething_a
global doSomething_b
doSomething():
end
The key is to track globals in the parser regardless of the target language and pass them along with non-global information to the language's template regardless. The target language's template file either processes the globals or it ignores them. A template receive enough information to define both types of languages (whether it uses it all or not), so there's no need to create a new parser.