Define and use a function within the same HAML file

Question

I've got a light-weight haml-based site that I'm building with Middleman (not Rails, but I'm tagging this with Rails because I think Rails people might know the answer).

Is it possible to define a function in-line in the haml file and then use it later in that same file?

(Yes, I know how to use separately-defined helper files. That's not the question.)

I have a page with a function that is uniquely specialized to that page. Defining it in a helper file is to me an unnecessary separation.

Example:

-def foo(color,text)
  -content_tag :p, style: "color: #{color}" do
    -text

%html
  %head
    %title Demo page

  %body
    %h1 demo page

    =foo("red", "this is red")
    =foo("blue", "this is blue")

Rendering the above page results in undefined method 'foo'.

Is there a way to make that work? (Did I define the function incorrectly?)

Answer 1

You have to define a singleton method:

:ruby
  def self.foo(color, text)
    content_tag :p, style: "color: #{color}" do
      text
    end
  end

%html
  %head
    %title Demo page
  %body
    %h1 demo page

    = foo("red", "this is red")

---

When you define foo it is defined as an instance method of Tilt::CompiledTemplates, but the template is evaluated in the context of a new Object which doesn't have foo. This is an abridged version of what this process looks like:

module Compiled; end

# code inside the `__tilt` method is a compiled haml code:
#   Haml::Template.compile(File.read('index.html.haml'), engine: Haml::Engine)
source = <<~CODE
  Compiled.class_eval do
    def __tilt_4220
      _buf = ""
      def foo(text)
        text
      end
      _buf << "<h1>demo page</h1>\n"
      _buf << foo("this is red")
      _buf
    end
  end
CODE

Object.class_eval(source)
method = Compiled.instance_method(:__tilt_4220)
# render
puts method.bind_call(Object.new)

https://github.com/jeremyevans/tilt/blob/v2.4.0/lib/tilt/template.rb#L192