Class: Baba::Scanner

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

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(source) ⇒ Scanner

Returns a new instance of Scanner.



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# File 'lib/baba/scanner.rb', line 9

def initialize(source)
  @source = source.strip
  @tokens = []

  @line = 1
  @current = 0
  @start = 0
end

Instance Attribute Details

#source ⇒ Object (readonly)

Returns the value of attribute source.



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# File 'lib/baba/scanner.rb', line 7

def source
  @source
end

#tokens ⇒ Object (readonly)

Returns the value of attribute tokens.



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# File 'lib/baba/scanner.rb', line 7

def tokens
  @tokens
end

Instance Method Details

#add_token(type, literal = nil) ⇒ Object 



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# File 'lib/baba/scanner.rb', line 33

def add_token(type, literal = nil)
  text = @source[@start...@current]
  @tokens << Token.new(type, text, literal, @line)
end

#advance ⇒ Object 



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# File 'lib/baba/scanner.rb', line 38

def advance
  @current += 1
  return @source[@current - 1]
end

#alpha?(c) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/baba/scanner.rb', line 65

def alpha?(c)
  !!(c =~ /([a-z]|[A-Z]|_)/)
end

#alphanumeric?(c) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/baba/scanner.rb', line 69

def alphanumeric?(c)
  alpha?(c) || digit?(c)
end

#digit?(c) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/baba/scanner.rb', line 61

def digit?(c)
  !!(c =~ /\d/)
end

#eof? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/baba/scanner.rb', line 18

def eof?
  @current >= @source.length
end

#error(c) ⇒ Object 



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# File 'lib/baba/scanner.rb', line 144

def error(c)
  Baba.scanner_error(@line, "Unexpected character '#{c}'", @source, @current)
end

#identifier ⇒ Object 



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# File 'lib/baba/scanner.rb', line 148

def identifier()
  while alphanumeric?(peek())
    advance()
  end

  text = @source[@start...@current]
  type = KEYWORDS[text]
  type = IDENTIFIER if type.nil?

  add_token(type)
end

#match(expected) ⇒ Object 



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# File 'lib/baba/scanner.rb', line 43

def match(expected)
  return false if eof?
  return false if @source[@current] != expected

  @current += 1
  return true
end

#number ⇒ Object 



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# File 'lib/baba/scanner.rb', line 176

def number()
  while digit?(peek())
    advance()
  end

  if peek() == "." && digit?(peek_next())
    advance()
    while digit?(peek())
      advance()
    end
  end

  add_token(NUMBER, @source[@start...@current].to_f)
end

#peek ⇒ Object 



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# File 'lib/baba/scanner.rb', line 51

def peek()
  return "\0" if eof?
  return source[@current]
end

#peek_next ⇒ Object 



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# File 'lib/baba/scanner.rb', line 56

def peek_next()
  return "\0" if (@current + 1 >= @source.length)
  @source[@current + 1]
end

#scan_token ⇒ Object 



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# File 'lib/baba/scanner.rb', line 73

def scan_token
  c = advance()
  case c
  when "("
    add_token(LEFT_PAREN)
  when ")"
    add_token(RIGHT_PAREN)
  when ","
    add_token(COMMA)
  when "-"
    add_token(MINUS)
  when "+"
    add_token(PLUS)
  when "*"
    add_token(STAR)
  when "/"
    add_token(SLASH)
  when ";"
    add_token(SEMICOLON)
  when ":"
    add_token(COLON)
  when "{"
    add_token(COLON)
  when "}"
    add_token(KEND)
  when "."
    add_token(DOT)
  when "!"
    add_token(match("=") ? NOT_EQUAL : NOT)
  when "<"
    add_token(match("=") ? LESS_EQUAL : LESS)
  when ">"
    add_token(match("=") ? GREATER_EQUAL : GREATER)
  when "="
    add_token(match("=") ? EQUAL_EQUAL : EQUAL)
  when "&"
    if match("&")
      add_token(AND)
    else
      error(c)
    end
  when "|"
    if match("|")
      add_token(OR)
    else
      error(c)
    end
  when "#"
    while peek() != "\n" && !eof?
      advance()
    end
  when " "
  when "\r"
    @line += 1
  when "\t"
    @line += 1
  when "\n"
    @line += 1
  when '"'
    string()
  else
    if digit?(c)
      number()
    elsif alpha?(c)
      identifier()
    else
      error(c)
    end
  end
end

#scan_tokens ⇒ Object 



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# File 'lib/baba/scanner.rb', line 22

def scan_tokens
  until eof?
    # We are at the next lexeme
    @start = @current
    scan_token()
  end

  add_token(EOF)
  return @tokens
end

#string ⇒ Object 



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# File 'lib/baba/scanner.rb', line 160

def string()
  while peek() != '"' && !eof?
    @line += 1 if peek() == '\n'
    advance()
  end

  if eof?
    Baba.scanner_error(@line, "Unterminated string", @source, @start)
  end

  advance()

  value = @source[(@start + 1)..(@current - 2)]
  add_token(STRING, value)
end