Class: Parser

Inherits:
Object
  • Object
show all
Defined in:
lib/parser.rb

Instance Method Summary collapse

Constructor Details

#initialize(istream) ⇒ Parser

Returns a new instance of Parser.



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# File 'lib/parser.rb', line 8

def initialize(istream)
  @scan = Scanner.new(istream)
  @todo = true
end

Instance Method Details

#Expr ⇒ Object 



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# File 'lib/parser.rb', line 30

def Expr() 
  return RestExpr(Term())
end

#ExprEWE ⇒ Object 



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# File 'lib/parser.rb', line 134

def ExprEWE()
  result = Term()
  result = RestExpr(result)
  return result
end

#Factor ⇒ Object

Raises:



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# File 'lib/parser.rb', line 95

def Factor() 
  t = @scan.getToken

  if t.type == :number then
    return NumNode.new(t.lex.to_i)
  end

  if t.type == :identifier then

    var = t.lex.to_s
    value = $calc.recallVar(t.lex.to_s)

    return IdentifierNod.new(var, value.to_i)
  end

  if t.type == :keyword then
    if t.lex == "R" then
      return RecallNode.new
    end
    if t.lex == "C" then
      $calc.store(0)
      return RecallNode.new
    end
  end
  if t.type == :lparen then
    
    expr = Expr()
    t = @scan.getToken

    if t.type == :rparen then
      return expr
    else
      raise ParseError.new
    end
  end

  raise ParseError.new
end

#parse ⇒ Object 



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# File 'lib/parser.rb', line 13

def parse()
  return Prog()
end

#Prog ⇒ Object

private private public protected



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# File 'lib/parser.rb', line 18

def Prog()
  result = Expr()
  t = @scan.getToken()
  
  if t.type != :eof then
    print "Expected EOF. Found ", t.type, ".\n"
    raise ParseError.new
  end
  
  return result
end

#RestExpr(e) ⇒ Object 



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# File 'lib/parser.rb', line 34

def RestExpr(e) 
  t = @scan.getToken()
  
  if t.type == :add then
       return RestExpr(AddNode.new(e,Term()))
  end
  
  if t.type == :sub then
    return RestExpr(SubNode.new(e,Term()))
  end
    
  @scan.putBackToken()
  
  return e
end

#RestTerm(e) ⇒ Object 



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# File 'lib/parser.rb', line 54

def RestTerm(e)
  t = @scan.getToken

  if t.type == :times then
    return RestTerm(TimesNode.new(e,Term()))
  end

  if t.type == :divide then
    return RestTerm(DivNode.new(e,Term()))
  end

  if t.type == :mod then
    return RestTerm(ModNode.new(e,Term()))
  end

  @scan.putBackToken
  return e
end

#Storable ⇒ Object 



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# File 'lib/parser.rb', line 73

def Storable()
    factor = Factor()

    t = @scan.getToken

    if t.type == :keyword then
      if t.lex == "S" then
        return StoreNode.new(factor)
      end
      if t.lex == "M" then
        return MNode.new(factor)
      end
      if t.lex == "P" then
        return PNode.new(factor)
      end
    end

    @scan.putBackToken

    factor
end

#Term ⇒ Object 



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# File 'lib/parser.rb', line 50

def Term()
  return RestTerm(Storable())
end