Syntax Highlighting (#218)

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Syntax Highlighting (# 218)

Namo namah Rubyists,

This week’s quiz is to write a syntax highlighter. Your program or
method will take as input unadorned Ruby code and return marked-up
code. Different syntactical elements of the code should have different
styles. As an additional challenge you may wish to indicate syntax
errors at the point in which they occur in the code. You may choose
any output style that you like. If you are unsure of what to use to
colorize output, then check out Term::ANSIColor1.

Have Fun!

On 8/23/09, Daniel M. [email protected] wrote:

This week’s quiz is to write a syntax highlighter. Your program or
method will take as input unadorned Ruby code and return marked-up
code. Different syntactical elements of the code should have different
styles. As an additional challenge you may wish to indicate syntax
errors at the point in which they occur in the code. You may choose
any output style that you like. If you are unsure of what to use to
colorize output, then check out Term::ANSIColor[1].

This was a fun little quiz. Of course, I cheated like mad. (I think
that was the point, tho.) My entry uses RubyLexer, my own stand-alone
lexer for ruby. It’ll be interesting to see what other submissions
look like.

This week’s quiz was solved by Caleb C…

Caleb used the RubyLexer gem to parse a Ruby file given as a command
line argument. Term::ANSIColor is used to color the tokens.

def coloruby file,fd=open(file)
  lexer=RubyLexer.new(file,fd)
  begin
    token=lexer.get1token
    print token.colorize
  end until RubyLexer::EoiToken===token
ensure
  print Term::ANSIColor.reset
end

The coloruby method uses RubyLexer to generate a stream of tokens.
Each token is then colorized and printed out. After all the tokens are
printed the color is reset with Term::ANSIColor.reset so that any
following text won’t receive collateral colorization.

So how are these tokens colorized anyway? Caleb’s solution opens up
the RubyLexer class and adds a colorize method to all tokens.
Term::ANSIColor is also included in the Token class so that all
the color methods are available as well.

class Token
  include Term::ANSIColor

  def colorize
    color+ident.to_s
  end
end

Each individual token class may define its own different color or
colorize method.

class MethNameToken
  alias color green
end

class KeywordToken
  def colorize
    if /[^a-z]/i===ident
      yellow+ident
    else
      red+ident
    end
  end
end

The end result is nice colorful Ruby code.1

Thank you Caleb for your solution to this week’s quiz!

Syntax Highlighting (#218) - Solutions

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