middleman で link_to_if っぽいことをやる

_nav.html.haml

-# source/partials/_nav.html.haml
%nav.nav
  %ul
    - data.nav.pages.each do |page|
      %li{ class: "#{'current' if page_classes == page.name}" }
        = page_classes == page.name ? page.label : (link_to page.label, "#{page.name}.html")

nav.yml

# data/nav.yml
pages:
  - name: 'index'
    label: 'ホーム'
  - name: 'concept'
    label: 'コンセプト'
  - name: 'products'
    label: '製品情報'
  - name: 'contact'
    label: 'お問い合わせ'