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

[Glenn Gillen]

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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