ERB/Templating clue for ruby - ruby

Question

Optimally I'd want template to look something like this:
interfaces {
<%= name %> {
description "<%= description %>";
mtu <%= mtu %>;
}
}
However, I'd want lines not to be printed if the code evaluates to non-true value. It could be hack to ERB, where after \n it sets print_line = true and after evaluating code with b%> to false it sets print_line = false, and only print if print_line.
But it seems changing ERB for this isn't exactly trivial, it reads whole template, non-code parts are inserted as print "data", and result is single big string of ruby code which is evaluated as whole during #result. I would either need to eval b%> code during string-scanning and just insert print "data" if it returns true, or nothing at all or I'd need to rescan the code in #result to run b%> first.
It seems bit fruitless to even use template, if you end up writing all of it inside code blocks, like:
interfaces {
<%= name %> {
<% if description %>
description "<%= description %>";
<% end%>
<% if mtu %>
mtu <%= mtu%>;
<% end%>
}
}
or:
interfaces {
<%= name %> {
<%= "description \"#{description}\";" if description %>
<%= "mtu #{mtu};" if mtu %>
}
}
I need to support various different configuration formats, in some other configuration format it might be 'maximum-transfer-unit <%= mtu> bytes'. I wish to keep all platform-specific intelligence in the template and actual code in the template minimum. I have no problem adding platform agnostic complexity outside the templates.
Seems like relatively common use-case. Before I go NIHing my own template language or hacking ERB, are there perhaps some other template language better fit for my use-case. Or missingsomething else?
I've implemented the hack for <%b stuff %> where whole line is omitted if that evaluates to false. ERB was not designed for anything like this at all so it's very dirty, and it may be better for me to just write my own template language, unless someone can suggest maybe existing solution where I can cleanly implement something like.
For interested parties, hack is here http://p.ip.fi/-NeJ
Ended up re-inventing the wheel: https://github.com/ytti/malline

Answer 1

Helper methods
def description_helper(description)
"description \"#{description}\";" if description
end
def mtu_helper(mtu)
"mtu #{mtu};" if mtu
end
interfaces {
<%= name %> {
<%= description_helper %>
<%= mtu_helper %>
}
}
Decorator pattern
class MyObject
def description
'some description'
end
def mtu
nil
end
module ViewDecorator
def description
"description \"#{super}\";" if super
end
def mtu
"mtu #{super};" if super
end
end
end
o = MyObject.new
p o.description #=> "some description"
p o.mtu #=> nil
o.extend MyObject::ViewDecorator
p o.description #=> "description \"some description\";"
p o.mtu #=> nil