Unable to parse APL Symbol using ANTLR - antlr

Question

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

Answer 1

"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)