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options {
  STATIC=true;
}

PARSER_BEGIN(UnitsParser)
package edu.mines.jtk.util;

import java.io.*;

/**
 * Parser (generated from UnitsParser.jj via JavaCC) to create Units 
 * from a string that conforms to the following (extended BNF) grammar:
 *  * unit -> expr EOF
 * expr -> term ( ("+" | "-") (DOUBLE|INTEGER) )?
 * term -> factor ( ("*")? factor | "/" factor )*
 * factor -> primary ("^" INTEGER)?
 * primary -> NAME | (DOUBLE|INTEGER) | "(" expr ")"
 * 
 *
 * @author Dave Hale
 * @version 1998.07.06
 */
final class UnitsParser {

  /** 
   * Parse a String containing a unit definition.
   * @param the unit definition, as in "coulomb/volt".
   * @exception ParseException if the definition is not valid.
   */
  static synchronized Units parse(String definition) throws ParseException {
    ReInit(new StringReader(definition));
    return units();
  }
}

PARSER_END(UnitsParser)

SKIP : {
    " "
  | "\t"
}

TOKEN : {
    < PLUS: "+" >
  | < MINUS: "-" >
  | < MUL: ("*"|".") >
  | < DIV: ("/"|"per"|"PER") >
  | < POW: ("^"|"**") >
  | < LP: "(" >
  | < RP: ")" >
  | < NAME: "%" | ()*(()+()+)* >
  | < INTEGER: ("-")?()+ >
  | < DOUBLE: ("-")?(["e","E"](["-","+"])?)? >
  | < #ALPHA:  | "_" >
  | < #LETTER: ["a"-"z","A"-"Z"] >
  | < #FLOAT:  | (".")? | "." >
  | < #DIGIT: ["0"-"9"] >
}

Units units() : {
  Units e;
} {
  e=expr()  {
    return e;
  }
}

Units expr() : { 
  Units t;
  Token n;
} {
  t=term() (
     (n=|n=) {
      t.shift(Double.valueOf(n.image).doubleValue());
    } |  (n=|n=) {
      t.shift(-Double.valueOf(n.image).doubleValue());
    }
  )? {
    return t;
  }
}

Units term() : {
  Units f,fb;
} {
  f=factor() (
    ()? fb=factor() {
      f.mul(fb);
    } |  fb=factor() {
      f.div(fb);
    }
  )* {
    return f;
  }
}

Units factor() : {
  Units p;
  Token n;
} {
  p=primary() (
     n= {
      p.pow(Integer.valueOf(n.image).intValue());
    }
  )? {
    return p;
  }
}

Units primary() : {
  Units e,p;
  Token n;
} {
  n= {
    p = Units.unitsFromName(n.image);
    if (p==null) throw new ParseException("Units \""+n.image+"\" are undefined.");
    return p;
  } | (n=|n=) {
    double d = (new Double(n.image)).doubleValue();
    return (new Units()).scale(d);
  } |  e=expr()  {
    return e;
  }
}