SXML is widely used when combining Scheme and the web, so the DSL has already been made for you, and is actually pretty pleasant to use.

Example SXML template, that fills in data fields from a given namespace:

    (form
     (@ (method (%data form-method))
        (action (%data form-action)))
     (label "Username")
     (input (@ (type "text")
               (name (%data username-input-name))))
     (label "Password")
     (input (@ (type "password")
               (name (%data password-input-name))))
     (input (@ (type "submit"))))