Linking CUP and jflex

Question

I am trying to link my parser.java and yylex.java using help from
http://www2.cs.tum.edu/projects/cup/examples.php
http://www.cs.princeton.edu/~appel/modern/java/CUP/manual.html
http://jflex.de/manual.html

But I am getting these errors.

error: Yylex is not abstract and does not override abstract method next_token() in Scanner

error: next_token() in Yylex cannot implement next_token() in Scanner

How to resolve them ?

My mini.flex file is:

import java.io.*; 

%%

%public
%cup 
%line
%column
%type int

identifier = {letter} ( {letter} | {decimal_digit} )*
letter        = [a-z] | "_"
decimal_digit = [0-9]

LineTerminator = \r|\n|\r\n
WhiteSpace     = {LineTerminator} | [ \t\f]
Comment = {GeneralComment} | {LineComment}
GeneralComment   = "/*"([^*]|\*+[^*/])*\*+"/"
LineComment     = "//" {LineTerminator}?

%%

<YYINITIAL> { 
"break" { return sym.breakd; }
"default" { return sym.defaultd; }
}

<YYINITIAL> {
  {identifier} { return sym.identifier; }
}

<YYINITIAL> { 
"+" {return sym.plus_op;}
"&" {return sym.amp_op;}
}

<YYINITIAL> { 
  {Comment}                      { /* ignore */ }
  \n                             { }
  {WhiteSpace}                   { /* ignore */ }
  [^]                            { /*Illegeal Character*/ }
}

My mini.cup file is:

// import java-cup-11b-runtime.*;

import java_cup.runtime.*;

parser code {: public Parser (java.io.Reader input) { super(new Yylex(input)); } :};

/* Preliminaries to set up and use the scanner.  */

/*init with {: scanner.init();              :};
scan with {: return scanner.next_token(); :};*/

terminal identifier;
terminal breakd, defaultd, plus_op, amp_op;

non terminal SourceFile, UnaryExpr, Expression, Statement, SimpleStmt, EmptyStmt, ExpressionStmt, unary_op;

    precedence left plus_op;

Expression ::= UnaryExpr | Expression plus_op UnaryExpr;
UnaryExpr  ::=  unary_op identifier;
unary_op   ::= plus_op | amp_op;

Statement ::= SimpleStmt;
SimpleStmt ::= EmptyStmt | ExpressionStmt;
EmptyStmt ::= ; // should be Empty
ExpressionStmt ::= Expression;

SourceFile ::= Statement;

I compile using:

java -jar java-cup-11b.jar -interface -parser Parser mini.cup
jflex mini.flex
javac -cp java-cup-11b-runtime.jar:. -Xlint *.java

The errors thrown are:

Parser.java:19: warning: [deprecation] lr_parser() in lr_parser has been deprecated public Parser() {super();}
^ Parser.java:22: warning: [deprecation] lr_parser(Scanner) in lr_parser has been deprecated public Parser(java_cup.runtime.Scanner s) {super(s);}
^ Parser.java:96: warning: [deprecation] lr_parser(Scanner) in lr_parser has been deprecated public Parser (java.io.Reader input) { super(new Yylex(input)); }
^ Parser.java:137: warning: [cast] redundant cast to Object Object start_val = (Object)((java_cup.runtime.Symbol) CUP$Parser$stack.elementAt(CUP$Parser$top-1)).value;
^ Yylex.java:12: error: Yylex is not abstract and does not override abstract method next_token() in Scanner
public class Yylex implements java_cup.runtime.Scanner { ^
Yylex.java:474: error: next_token() in Yylex cannot implement next_token() in Scanner
public int next_token() throws java.io.IOException {
^ return type int is not compatible with Symbol
Yylex.java:631: error: incompatible types
{ return new java_cup.runtime.Symbol(sym.EOF); }
^ required: int
found: Symbol
3 errors
4 warnings

rds rds · Accepted Answer · 2015-04-12T17:01:04

The problem is that next_token() doesn't compile because:

return type int is not compatible with Symbol

and

Yylex.java:631: error: incompatible types
{ return new java_cup.runtime.Symbol(sym.EOF); }
^ required: int
found: Symbol

The generated code is

public int next_token() throws java.io.IOException {
...
if (c) {
  // sometimes returns a Symbol
  return new java_cup.runtime.Symbol(sym.EOF);
} else {
  // sometimes returns an int
  return sym.identifier;
}

From the documentation:

The %type directive overrides settings of the %cup switch.

Solution: Remove the %type int directive from mini.jflex (and use cup's java_cup.runtime.Symbol).

Linking CUP and jflex

1 Answers