[LRUG] DSLs for newbies: HTML generation (discuss)

[Roland Swingler]

or erector

http://erector.rubyforge.org

On Thu, Dec 10, 2009 at 2:17 PM, Glenn Gillen <glenn at rubypond.com> wrote:
> Or Markaby:
>
> http://markaby.rubyforge.org/
>
> On 10 Dec 2009, at 13:56, Alex Graul wrote:
>
>> That's very close to the syntax of Builder, see http://builder.rubyforge.org/
>>
>> Cheers,
>> Alex
>>
>> On 10 Dec 2009, at 13:49, Daniel Barlow wrote:
>>
>>> I'm playing with Ruby for the first time (pretty much) and having seen haml I thought it would be fun to play with alternate syntaxes.  This one has much less in the way of funny characters (% and #) and isn't whitespace-sensitive
>>>
>>> It's probably also a really dumb idea.  Like I say, first time Ruby programmer.  Anyway, here's a motivating example of its use
>>>
>>> h=HTML.new
>>> def h.content
>>> html do
>>>   head { title(:id=>123) {"My page title" }}
>>>   body do
>>>     div do
>>>       h1(:class => "fancy_formatted") {"hello world"}
>>>       text "some stuff","more stuff"
>>>       ul {
>>>         %w(red orange yellow green blue indigo violent).map {|name|
>>>           li { text name }
>>>         }
>>>       }
>>>     end
>>>   end
>>> end
>>> end
>>> h.output
>>>
>>> It's all valid Ruby code.  There is a method (implemented with method_missing) for each HTML element: when called it expects HTML arguments as attributes and a block of element content: it outputs the markup for the start-tag/end-tag and calls the block.
>>>
>>> Inside the block you can call more element-making methods, and/or you can call #text (as shown) to output plain text, and/or you can return some (preferably string) value which will also be output as if by #text
>>>
>>> So,
>>> - a neat hack?
>>> - an offence against (your choice of) god?
>>> - dull and unoriginal and every other newbie did exactly the same thing when learning?
>>> - really ugly ruby style?
>>>
>>> All criticism welcome.  I'm a Lisp programmer in my day job, so I've almost certainly heard worse.
>>>
>>> Oh, the implementation?  The HTML it generates is not entirely valid (attribute quoting and empty elements are two obvious omissions: introducing all that whitespace, I hazily remember from reading SGML specs back in the day, is probably also wrong) and indenting is hacky, but you get the gist.  It's more about proof-of-concept and playing with the DSL syntax at this stage than production-quality output
>>>
>>> Is Hash.map supposed to work like that, or is it accidental?  It's dashed useful, that I will say
>>>
>>> ---cut here---
>>> class HTML
>>> # this is a partial list for testing, and obviously needs to
>>> # be extending to all tags in whatever version of HTML you want
>>> # to produce
>>> @@allowed_tags=%w(html head title body h1 h2 h3 h4 h5 h6
>>>                   p div span ul li).map {|n| n.to_sym}
>>>
>>> def texts(stuff)
>>>   stuff and
>>>     stuff.each {|x| x and @content << ("\n"+(" " * @indent)+x) }
>>>   nil
>>> end
>>>
>>> def text(*stuff)
>>>   texts stuff
>>> end
>>>
>>> def method_missing(name,*args,&body)
>>>   if @@allowed_tags.member?(name)
>>>     attributes = args[0] || [];
>>>     text "<#{name}"+attributes.map {|k,v| " "+k.to_s+"="+v.to_s }.to_s + ">"
>>>     @indent=@indent+4;
>>>     texts body.call
>>>     @indent=@indent-4;
>>>     text "</#{name}>"
>>>   else
>>>     super # not on our list, let it raise UndefinedMethodError
>>>   end
>>> end
>>>
>>> def output
>>>   @content=[]
>>>   @indent=0
>>>   content
>>>   print @content
>>>   puts
>>> end
>>> end
>>> ---cut here---
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>>
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