Problems installing rdoc, irb, bluecloth, chronic on fedora 12

Question

What do these errors mean?

[root@localhost config]# gem install bluecloth
Building native extensions.  This could take a while...
ERROR:  Error installing bluecloth:
    ERROR: Failed to build gem native extension.

/usr/bin/ruby extconf.rb
can't find header files for ruby.


Gem files will remain installed in /usr/lib64/ruby/gems/1.8/gems/bluecloth-2.0.7 for 
inspection.
Results logged to /usr/lib64/ruby/gems/1.8/gems/bluecloth-2.0.7/ext/gem_make.out
[root@localhost config]# 

And this

[root@localhost config]# gem install chronic
Successfully installed json_pure-1.4.3
Successfully installed rubyforge-2.0.4
Successfully installed hoe-2.6.0
Successfully installed chronic-0.2.3
4 gems installed
/usr/lib64/ruby/gems/1.8/gems/rdoc-2.5.8/lib/rdoc/ruby_lex.rb:67: warning: 
parenthesize argument(s) for future version
ERROR:  While executing gem ... (Gem::DocumentError)
    ERROR: RDoc documentation generator not installed: no such file to load -- irb/slex
[root@localhost config]# 

I have installed rdocs using "yum install ruby-rdocs". But I don't understand what this error means

Answer 1

yum install ruby-devel ruby-irb ruby-rdoc ruby-ri

Although the former command fixes both issues, take in mind that in the case of the second error message, you can had also skip the documentation by adding --no-rdoc.

April 2017:
--[no-]rdoc argument has been deprecated as explained in gem install --help. You now have to use --no-document at each gem installation or store this in your ~/.gemrc as explained in this answer.