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 7

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

Instance Method Details

#Expr ⇒ Object 



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# File 'lib/parser.rb', line 28

def Expr() 
  return RestExpr(Term())
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 == :keyword then
    if t.lex == "R" then
      return RecallNode.new
    else
      raise ParseError.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 11

def parse()
  return Prog()
end

#Prog ⇒ Object

private



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# File 'lib/parser.rb', line 16

def Prog()
  result = Expr()
  t = @scan.getToken()
  
  unless 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 32

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()
  
  e
end

#RestTerm(e) ⇒ Object 



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# File 'lib/parser.rb', line 65

def RestTerm(e)
  t = @scan.getToken
  
  if t.type == :times then
    return RestTerm(TimesNode.new(e, Storable()))
  end
  if t.type == :divide then
    return RestTerm(DivideNode.new(e, Storable()))
  end
  
  @scan.putBackToken    
  e        
end

#Storable ⇒ Object 



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# File 'lib/parser.rb', line 79

def Storable()
  fact = Factor()
  t = @scan.getToken

  if t.type == :keyword then
    if t.lex == "S" then
      return StoreNode.new(fact)
    else
      raise ParseError.new
    end
  end

  @scan.putBackToken
  fact
end

#Term ⇒ Object 



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# File 'lib/parser.rb', line 48

def Term()
  RestTerm(Storable())
  # Write your Term() code here. This code is just temporary
  # so you can try the calculator out before finishing it.
  
  # t = @scan.getToken()
  
  # if t.type == :number then
  #   val = t.lex.to_i
  #   return NumNode.new(val)
  # end
  
  # puts "Term not implemented\n"
  
  # raise ParseError.new
end