From: Peter Suk <peter.kwangjun.suk@...>
Date: 2005-04-25T06:06:10+09:00
Subject: Racc

Folks,

I need help using Racc.  I've been trying to go through the basic 
calculator example, but no go.  The grammar is processed without any 
shift-reduce conflicts.  It appears I am feeding the wrong kind of 
tokens to it.  I keep getting:


Parsing file:
/usr/local/lib/ruby/site_ruby/1.8/racc/parser.rb:377:in `on_error':  
(Racc::ParseError)
parse error on value 1 (NUMBER) from 
/usr/local/lib/ruby/site_ruby/1.8/racc/parser.rb:104:in 
`_racc_do_parse_c'
         from /usr/local/lib/ruby/site_ruby/1.8/racc/parser.rb:104:in 
`__send__'
         from /usr/local/lib/ruby/site_ruby/1.8/racc/parser.rb:104:in 
`do_parse'
         from racc-calc-2.y:47:in `parse'
         from ruby_calc_test.rb:20


I am feeding it tokens that are two-element arrays, as stated in the 
documentation.  <http://i.loveruby.net/en/man/racc/parser.html>  But it 
is not at all clear what should be in the second element.


tokens = [  [ :NUMBER, 1 ],
			[ :PLUS, "+" ],
			[ :NUMBER, 2 ],
			[ false, false ] ]


--Peter


--
There's neither heaven nor hell, save what we grant ourselves.
There's neither fairness nor justice, save what we grant each other.


-------- ruby_calc_test.rb --------
#!/usr/bin/ruby
require "FakeLexer"
require "RubyCalcParser"

## reuse the same parser object


p = RubyCalcParser.new
#p.yydebug = true
#p.yyerror = $stdout

print "Parsing file:\n"

tokens = [  [ :NUMBER, 1 ],
			[ :PLUS, "+" ],
			[ :NUMBER, 2 ],
			[ false, false ] ]

p.lexer = FakeLexer.new(tokens)
print(p.parse.inspect)

print "\n"
-------- racc-calc-2.y --------
class RubyCalcParser


prechigh
   left TIMES DIVIDE
   left PLUS MINUS
preclow


token	NUMBER PLUS MINUS TIMES DIVIDE LPAREN RPAREN


rule

	
	exp:    NUMBER               { TestNumNode.new($1, "+") }
			| exp PLUS exp       { TestBinaryOpNode.new($1, "+", $3) }
			| exp MINUS exp      { TestBinaryOpNode.new($1, "-", $3) }
			| exp TIMES exp      { TestBinaryOpNode.new($1, "*", $3) }
			| exp DIVIDE exp        { TestBinaryOpNode.new($1, "/", $3) }
			| LPAREN exp RPAREN     { TestExpNode.new($2) }
			| LPAREN error RPAREN	{ 1 } ## example error recovery--a bad 
expression is interpreted as a 1
	;

end # RubyCalcParser


---- header ----
require 'RubyCalcAst'

---- inner ----

def initialize
	@ast = nil
end

attr_accessor :lexer ;

   def parse()
     return do_parse()
   end

protected

def next_token
     return @lexer.yylex()
end
-------- RubyCalcAst.rb --------
class TestNumNode
     def initialize(num, sign)
		@num = num
		@sign = sign
     end
end
class TestBinaryOpNode
	def initialize(term1, op, term2)
		@term1 = term1
		@op = op
		@term2 = term2
     end
end
class TestExpNode
     def initialize(exp)
		@exp = exp
     end
end
-------- FakeLexer.rb --------
require 'RubyCalcParser'

class FakeLexer

     def initialize(tokens)
		@tokens = tokens
		@index = 0
     end

     def reset()
		@index = 0
     end

     def yylex()
		rval = @tokens[@index]
		@index += @index
		return rval
     end

end
-------- end --------