Unable to parse APL Symbol using ANTLR - antlr

I am trying to parse APL expressions using ANTLR, It is sort of APL source code parser. It parse normal characters but fails to parse special symbols(like '←')
expression = N←0
Lexer
/* Lexer Tokens. */
NUMBER:
(DIGIT)+ ( '.' (DIGIT)+ )?;
ASSIGN:
'←'
;
DIGIT :
[0-9]
;
Output:
[#0,0:1='99',<NUMBER>,1:0]
**[#1,4:6='â??',<'â??'>,2:0**]
[#2,7:6='<EOF>',<EOF>,2:3]
Can some one help me to parse special characters from APL language.
I am following below steps.
Written Grammar
"antlr4.bat" used to generate parser from grammar.
"grun.bat" is used to generate token

"grun.bat" is used to generate token
That just means your terminal cannot display the character properly. There is nothing wrong with the generated parser or lexer not being able to recognise ←.
Just don't use the bat file, but rather test your lexer and parser by writing a small class yourself using your favourite IDE (which can display the characters properly).
Something like this:
grammar T;
expression
: ID ARROW NUMBER
;
ID : [a-zA-Z]+;
ARROW : '←';
NUMBER : [0-9]+;
SPACE : [ \t\r\n]+ -> skip;
and a main class:
import org.antlr.v4.runtime.*;
public class Main {
public static void main(String[] args) {
TLexer lexer = new TLexer(CharStreams.fromString("N ← 0"));
TParser parser = new TParser(new CommonTokenStream(lexer));
System.out.println(parser.expression().toStringTree(parser));
}
}
which will display:
(expression N ← 0)
EDIT
You could also try using the unicode escape for the arrow like this:
grammar T;
expression
: ID ARROW NUMBER
;
ID : [a-zA-Z]+;
ARROW : '\u2190';
NUMBER : [0-9]+;
SPACE : [ \t\r\n]+ -> skip;
and the Java class:
import org.antlr.v4.runtime.*;
public class Main {
public static void main(String[] args) {
String source = "N \u2190 0";
TLexer lexer = new TLexer(CharStreams.fromString(source));
TParser parser = new TParser(new CommonTokenStream(lexer));
System.out.println(source + ": " + parser.expression().toStringTree(parser));
}
}
which will print:
N ← 0: (expression N ← 0)

Related

No way to implement a q quoted string with custom delimiters in Antlr4

I'm trying to implement a lexer rule for an oracle Q quoted string mechanism where we have something like q'$some string$'
Here you can have any character in place of $ other than whitespace, (, {, [, <, but the string must start and end with the same character. Some examples of accepted tokens would be:
q'!some string!'
q'ssome strings'
Notice how s is the custom delimiter but it is fine to have that in the string as well because we would only end at s'
Here's how I was trying to implement the rule:
Q_QUOTED_LITERAL: Q_QUOTED_LITERAL_NON_TERMINATED . QUOTE-> type(QUOTED_LITERAL);
Q_QUOTED_LITERAL_NON_TERMINATED:
Q QUOTE ~[ ({[<'"\t\n\r] { setDelimChar( (char)_input.LA(-1) ); }
( . { !isValidEndDelimChar() }? )*
;
I have already checked the value I get from !isValidEndDelimChar() and I'm getting a false predicate here at the right place so everything should work, but antlr simply ignores this predicate. I've also tried moving the predicate around, putting that part in a separate rule, and a bunch of other stuff, after a day and a half of research on the same I'm finally raising this issue.
I have also tried to implement it in other ways but there doesn't seem to be a way to implement a custom char delimited string in antlr4 (The antlr3 version used to work).
Not sure why the { ... } action isn't invoked, but it's not needed. The following grammar worked for me (put the predicate in front of the .!):
grammar Test;
#lexer::members {
boolean isValidEndDelimChar() {
return (_input.LA(1) == getText().charAt(2)) && (_input.LA(2) == '\'');
}
}
parse
: .*? EOF
;
Q_QUOTED_LITERAL
: 'q\'' ~[ ({[<'"\t\n\r] ( {!isValidEndDelimChar()}? . )* . '\''
;
SPACE
: [ \t\f\r\n] -> skip
;
If you run the class:
import org.antlr.v4.runtime.*;
public class Main {
public static void main(String[] args) {
Lexer lexer = new TestLexer(CharStreams.fromString("q'ssome strings' q'!foo!'"));
CommonTokenStream tokens = new CommonTokenStream(lexer);
tokens.fill();
for (Token t : tokens.getTokens()) {
System.out.printf("%-20s %s\n", TestLexer.VOCABULARY.getSymbolicName(t.getType()), t.getText());
}
}
}
the following output will be printed:
Q_QUOTED_LITERAL q'ssome strings'
Q_QUOTED_LITERAL q'!foo!'
EOF <EOF>

how to report grammar ambiguity in antlr4

According to the antlr4 book (page 159), and using the grammar Ambig.g4, grammar ambiguity can be reported by:
grun Ambig stat -diagnostics
or equivalently, in code form:
parser.removeErrorListeners();
parser.addErrorListener(new DiagnosticErrorListener());
parser.getInterpreter().setPredictionMode(PredictionMode.LL_EXACT_AMBIG_DETECTION);
The grun command reports the ambiguity properly for me, using antlr-4.5.3. But when I use the code form, I dont get the ambiguity report. Here is the command trace:
$ antlr4 Ambig.g4 # see the book's page.159 for the grammar
$ javac Ambig*.java
$ grun Ambig stat -diagnostics < in1.txt # in1.txt is as shown on page.159
line 1:3 reportAttemptingFullContext d=0 (stat), input='f();'
line 1:3 reportAmbiguity d=0 (stat): ambigAlts={1, 2}, input='f();'
$ javac TestA_Listener.java
$ java TestA_Listener < in1.txt # exits silently
The TestA_Listener.java code is the following:
import org.antlr.v4.runtime.*;
import org.antlr.v4.runtime.atn.*; // for PredictionMode
import java.util.*;
public class TestA_Listener {
public static void main(String[] args) throws Exception {
ANTLRInputStream input = new ANTLRInputStream(System.in);
AmbigLexer lexer = new AmbigLexer(input);
CommonTokenStream tokens = new CommonTokenStream(lexer);
AmbigParser parser = new AmbigParser(tokens);
parser.removeErrorListeners(); // remove ConsoleErrorListener
parser.addErrorListener(new DiagnosticErrorListener());
parser.getInterpreter().setPredictionMode(PredictionMode.LL_EXACT_AMBIG_DETECTION);
parser.stat();
}
}
Can somebody please point out how the above java code should be modified, to print the ambiguity report?
For completeness, here is the code Ambig.g4 :
grammar Ambig;
stat: expr ';' // expression statement
| ID '(' ')' ';' // function call statement
;
expr: ID '(' ')'
| INT
;
INT : [0-9]+ ;
ID : [a-zA-Z]+ ;
WS : [ \t\r\n]+ -> skip ;
And here is the input file in1.txt :
f();
Antlr4 is a top-down parser, so for the given input, the parse match is unambiguously:
stat -> expr -> ID -> ( -> ) -> stat(cnt'd) -> ;
The second stat alt is redundant and never reached, not ambiguous.
To resolve the apparent redundancy, a predicate might be used:
stat: e=expr {isValidExpr($e)}? ';' #exprStmt
| ID '(' ')' ';' #funcStmt
;
When isValidExpr is false, the function statement alternative will be evaluated.
I waited for several days for other people to post their answers. Finally after several rounds of experimenting, I found an answer:
The following line should be deleted from the above code. Then we get the same ambiguity report as given by grun.
parser.removeErrorListeners(); // remove ConsoleErrorListener
The following code will be work
public static void main(String[] args) throws IOException {
CharStream input = CharStreams.fromStream(System.in);
AmbigLexer lexer = new AmbigLexer(input);
CommonTokenStream tokens = new CommonTokenStream(lexer);
AmbigParser parser = new AmbigParser(tokens);
//parser.removeErrorListeners(); // remove ConsoleErrorListener
parser.addErrorListener(new org.antlr.v4.runtime.DiagnosticErrorListener()); // add ours
parser.getInterpreter().setPredictionMode(PredictionMode.LL_EXACT_AMBIG_DETECTION);
parser.stat(); // parse as usual
}

ANTLR Is it possible to make grammar with embed grammar inside?

ANTLR: Is it possible to make grammar with embed grammar (with it's own lexer) inside?
For example in my language I have ability to use embed SQL language:
var Query = [select * from table];
with Query do something ....;
Is it possible with ANTLR?
Is it possible to make grammar with embed grammar (with it's own lexer) inside?
If you mean whether it is possible to define two languages in a single grammar (using separate lexers), then the answer is: no, that's not possible.
However, if the question is whether it is possible to parse two languages into a single AST, then the answer is: yes, it is possible.
You simply need to:
define both languages in their own grammar;
create a lexer rule in you main grammar that captures the entire input of the embedded language;
use a rewrite rule that calls a custom method that parses the external AST and inserts it in the main AST using { ... } (see the expr rule in the main grammar (MyLanguage.g)).
MyLanguage.g
grammar MyLanguage;
options {
output=AST;
ASTLabelType=CommonTree;
}
tokens {
ROOT;
}
#members {
private CommonTree parseSQL(String sqlSrc) {
try {
MiniSQLLexer lexer = new MiniSQLLexer(new ANTLRStringStream(sqlSrc));
MiniSQLParser parser = new MiniSQLParser(new CommonTokenStream(lexer));
return (CommonTree)parser.parse().getTree();
} catch(Exception e) {
return new CommonTree(new CommonToken(-1, e.getMessage()));
}
}
}
parse
: assignment+ EOF -> ^(ROOT assignment+)
;
assignment
: Var Id '=' expr ';' -> ^('=' Id expr)
;
expr
: Num
| SQL -> {parseSQL($SQL.text)}
;
Var : 'var';
Id : ('a'..'z' | 'A'..'Z')+;
Num : '0'..'9'+;
SQL : '[' ~']'* ']';
Space : ' ' {skip();};
MiniSQL.g
grammar MiniSQL;
options {
output=AST;
ASTLabelType=CommonTree;
}
parse
: '[' statement ']' EOF -> statement
;
statement
: select
;
select
: Select '*' From ID -> ^(Select '*' From ID)
;
Select : 'select';
From : 'from';
ID : ('a'..'z' | 'A'..'Z')+;
Space : ' ' {skip();};
Main.java
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 src = "var Query = [select * from table]; var x = 42;";
MyLanguageLexer lexer = new MyLanguageLexer(new ANTLRStringStream(src));
MyLanguageParser parser = new MyLanguageParser(new CommonTokenStream(lexer));
CommonTree tree = (CommonTree)parser.parse().getTree();
DOTTreeGenerator gen = new DOTTreeGenerator();
StringTemplate st = gen.toDOT(tree);
System.out.println(st);
}
}
Run the demo
java -cp antlr-3.3.jar org.antlr.Tool MiniSQL.g
java -cp antlr-3.3.jar org.antlr.Tool MyLanguage.g
javac -cp antlr-3.3.jar *.java
java -cp .:antlr-3.3.jar Main
Given the input:
var Query = [select * from table]; var x = 42;
the output of the Main class corresponds to the following AST:
And if you want to allow string literals inside your SQL (which could contain ]), and comments (which could contain ' and ]), the you could use the following SQL rule inside your main grammar:
SQL
: '[' ( ~(']' | '\'' | '-')
| '-' ~'-'
| COMMENT
| STR
)*
']'
;
fragment STR
: '\'' (~('\'' | '\r' | '\n') | '\'\'')+ '\''
| '\'\''
;
fragment COMMENT
: '--' ~('\r' | '\n')*
;
which would properly parse the following input in a single token:
[
select a,b,c
from table
where a='A''B]C'
and b='' -- some ] comment ] here'
]
Just beware that trying to create a grammar for an entire SQL dialect (or even a large subset) is no trivial task! You may want to search for existing SQL parsers, or look at the ANTLR wiki for example-grammars.
Yes, with AntLR it is called Island grammar.
You can get a working example in the v3 examples, inside the island-grammar folder : it shows the usage of a grammar to parse javadoc comments inside of java code.
You can also find some clues in the doc Island Grammars Under Parser Control and that Another one.

ANTLR, heterogeneous AST problem

I examine heterogeneous trees in ANTLR (using ANTLRWorks 1.4.2).
Here is the example of what I have already done in ANTLR.
grammar test;
options {
language = java;
output = AST;
}
tokens {
PROGRAM;
VAR;
}
#members {
class Program extends CommonTree {
public Program(int ttype) {
token = new CommonToken(ttype, "<start>");
}
}
}
start
: program var function
// Works fine:
//-> ^(PROGRAM program var function)
// Does not work (described below):
-> ^(PROGRAM<Program> program var function)
;
program
: 'program'! ID ';'!
;
var
: TYPE^ ID ';'!
;
function
: ID '('! ')'! ';'!
;
TYPE
: 'int'
| 'string'
;
ID
: ('a'..'z' | 'A'..'Z')+
;
WHITESPACE
: (' ' | '\t' '\n'| '\r' | '\f')+ {$channel = HIDDEN;}
;
Sample input:
program foobar;
int foo;
bar();
When I use rewrite rule ^(PROGRAM<Program> program var function), ANTLR stumbles over and I get AST like this:
Whereas when I use this rewrite rule ^(PROGRAM program var function) it works:
Could anyone explain where am I wrong, please? Frankly, I do not really get the idea of heterogeneous trees and how do I use <…> syntax in ANTLR.
What do r0 and r1 mean (first picture)?
I have no idea what these r0 and r1 mean: I don't use ANTLRWorks for debugging, so can't comment on that.
Also, language = java; causes ANTLR 3.2 to produce the error:
error(10): internal error: no such group file java.stg
error(20): cannot find code generation templates java.stg
error(10): internal error: no such group file java.stg
error(20): cannot find code generation templates java.stg
ANTLR 3.2 expects it to be language = Java; (capital "J"). But, by default the target is Java, so, mind as well remove the language = ... entirely.
Now, as to you problem: I cannot reproduce it. As I mentioned, I tested it with ANTLR 3.2, and removed the language = java; part from your grammar, after which everything went as (I) expected.
Enabling the rewrite rule -> ^(PROGRAM<Program> program var function) produces the following ATS:
and when enabling the rewrite rule -> ^(PROGRAM program var function) instead, the following AST is created:
I tested both rewrite rules this with the following class:
import org.antlr.runtime.*;
import org.antlr.runtime.tree.*;
import org.antlr.stringtemplate.*;
public class Main {
public static void main(String[] args) throws Exception {
ANTLRStringStream in = new ANTLRStringStream("program foobar; int foo; bar();");
testLexer lexer = new testLexer(in);
CommonTokenStream tokens = new CommonTokenStream(lexer);
testParser parser = new testParser(tokens);
testParser.start_return returnValue = parser.start();
CommonTree tree = (CommonTree)returnValue.getTree();
DOTTreeGenerator gen = new DOTTreeGenerator();
StringTemplate st = gen.toDOT(tree);
System.out.println(st);
}
}
And the images are produced using graph.gafol.net (and the output of the Main class, of course).

ANTLR : How to replace all characters defined as space with actual space

My ANTLR code is as follow :
LPARENTHESIS : ('(');
RPARENTHESIS : (')');
fragment CHARACTER : ('a'..'z'|'0'..'9'|);
fragment QUOTE : ('"');
fragment WILDCARD : ('*');
fragment SPACE : (' '|'\n'|'\r'|'\t'|'\u000C'|';'|':'|',');
WILD_STRING
: (CHARACTER)*
(
('?')
(CHARACTER)*
)+
;
PREFIX_STRING
: (CHARACTER)+
(
('*')
)+
;
WS : (SPACE) { $channel=HIDDEN; };
PHRASE : (QUOTE)(LPARENTHESIS)?(WORD)(WILDCARD)?(RPARENTHESIS)?((SPACE)+(LPARENTHESIS)?(WORD)(WILDCARD)?(RPARENTHESIS)?)*(SPACE)+(QUOTE);
WORD : (CHARACTER)+;
What I would like to do is to replace all characters marked as space to be replaced with actual space character in the PHRASE. Also if possible, I would then like all continuous spaces to be represented by a single space.
Any help would be most appreciated. For some reason, I am finding it hard to understand ANTLR. Any good tutorials out there ?
Java
Invoke your lexer's setText(...) method:
grammar T;
parse
: words EOF {System.out.println($words.text);}
;
words
: Word (Spaces Word)*
;
Word
: ('a'..'z'|'A'..'Z')+
;
Spaces
: (' ' | '\t' | '\r' | '\n')+ {setText(" ");}
;
Which can be tested with the class:
import org.antlr.runtime.*;
public class Main {
public static void main(String[] args) throws Exception {
String source = "This is \n just \t\t\t\t\t\t a \n\t\t test";
ANTLRStringStream in = new ANTLRStringStream(source);
TLexer lexer = new TLexer(in);
CommonTokenStream tokens = new CommonTokenStream(lexer);
TParser parser = new TParser(tokens);
System.out.println("------------------------------\nSource:\n" + source +
"\n------------------------------\nAfter parsing:");
parser.parse();
}
}
which produces the following output:
------------------------------
Source:
This is
just a
test
------------------------------
After parsing:
This is just a test
Puneet Pawaia wrote:
Any help would be most appreciated. For some reason, I am finding it hard to understand ANTLR. Any good tutorials out there ?
The ANTLR Wiki has loads of informative info, albeit a bit unstructured (but that could just be me!).
The best ANTLR tutorial is the book: The Definitive ANTLR Reference: Building Domain-Specific Languages.
C#
For the C# target, try this:
grammar T;
options {
language=CSharp2;
}
#parser::namespace { Demo }
#lexer::namespace { Demo }
parse
: words EOF {Console.WriteLine($words.text);}
;
words
: Word (Spaces Word)*
;
Word
: ('a'..'z'|'A'..'Z')+
;
Spaces
: (' ' | '\t' | '\r' | '\n')+ {Text = " ";}
;
with the test class:
using System;
using Antlr.Runtime;
namespace Demo
{
class MainClass
{
public static void Main (string[] args)
{
ANTLRStringStream Input = new ANTLRStringStream("This is \n just \t\t\t\t\t\t a \n\t\t test");
TLexer Lexer = new TLexer(Input);
CommonTokenStream Tokens = new CommonTokenStream(Lexer);
TParser Parser = new TParser(Tokens);
Parser.parse();
}
}
}
which also prints This is just a test to the console. I tried to use SetText(...) instead of setText(...) but that didn't work either, and the C# API docs are currently off-line, so I used the trial and error-hack {Text = " ";}. I tested it with the C# 3.1.1 runtime DLL's.
Good luck!