Windowsへのhpricotのインストールではまった。

pikをビルドしようとしたら、hpricotがなくて怒られた。
そこで、hpricotを入れようとしたのだが、単純にgem install hpricotとしても、以下のようなエラーがでてくる。

$ gem install hpricot -v 0.8.3
Building native extensions.  This could take a while...
ERROR:  Error installing hpricot:
        ERROR: Failed to build gem native extension.

J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/bin/ruby.exe extconf.rb
checking for stdio.h... *** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of
necessary libraries and/or headers.  Check the mkmf.log file for more
details.  You may need configuration options.

Provided configuration options:
        --with-opt-dir
        --without-opt-dir
        --with-opt-include
        --without-opt-include=${opt-dir}/include
        --with-opt-lib
        --without-opt-lib=${opt-dir}/lib
        --with-make-prog
        --without-make-prog
        --srcdir=.
        --curdir
        --ruby=J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/bin/ruby
J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:368:in `try_do': The complier failed to generate
an executable file. (RuntimeError)
You have to install development tools first.
        from J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:452:in `try_cpp'
        from J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:834:in `block in have_header'
        from J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:693:in `block in checking_for'
        from J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:280:in `block (2 levels) in postpone'
        from J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:254:in `open'
        from J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:280:in `block in postpone'
        from J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:254:in `open'
        from J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:276:in `postpone'
        from J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:692:in `checking_for'
        from J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/1.9.1/mkmf.rb:833:in `have_header'
        from extconf.rb:2:in `<main>'


Gem files will remain installed in J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/gems/1.9.1/gems/hpricot-0.8.3 for inspection.
Results logged to J:/developments/environments/Ruby/.pik/Ruby-192dev-preview3-1/lib/ruby/gems/1.9.1/gems/hpricot-0.8.3/ext/fast_xs/gem_make.out

いろいろ調べたら、ここに情報がのっていた。--> ソース

つまりは、--platform=mswin32 というオプションを付ければよかったのです。

$ gem install hpricot -v 0.8.3 --platform=mswin32
Successfully installed hpricot-0.8.3-x86-mswin32
1 gem installed
Installing ri documentation for hpricot-0.8.3-x86-mswin32...
Installing RDoc documentation for hpricot-0.8.3-x86-mswin32...

これで解決。