‘Iacta alea est’
In a previous post we read a template written in the Hypertext DSL from file and successfully executed it in our context with variables and helpers.
In this post I want to continue down that path and see if we can integrate reading a layout and partials from file and then compile them together with the template. We can use our previous experiments in nested templating with Hypertext as a guide while using our initial code (from yesterday) as a starting point:
class Context < Hypertext::DSL
def initialize(params, fragment)
params.each do |key, val|
instance_variable_set(sprintf("@%s", key), val)
end
@ht = Hypertext.new
instance_eval fragment
end
end
class Template < Context
def id_generator
"id-#{rand(100)}"
end
end
We could of course mimic the approach with Sew and Syro with a double pass and two Template classes. Assuming the following layout and template (no partials):
# layout.ht
html lang: "en-GB" do
head do
title do
text @page_title
end
end
body do
append content
end
end
# template.ht
p do
text "A Hypertext template."
end
Then applying this approach as before, but instead loading everything in from file:
params = { page_title: "Hello, World!" }
template = Template.new(params, File.read("template.ht"))
layout = Template.new(
params.merge(content: template.to_s),
File.read("layout.ht"))
puts layout.to_s
This gives us the desired output, with the template nested inside the layout and rendering the HTML.
# =>
# <html lang="en-GB">
# <head>
# <title>
# Hello, World!
# </title>
# </head>
# <body>
# <p>
# A Hypertext template.
# </p>
#
# </body>
# </html>
Before I explore a way to render the layout in the same Template class let’s take a look at partials. Instead of calling a helper method which contains the hypertext definition as before:
class Template < Context
…
def heading
h1 id: id_generator do
text "Welcome"
end
end
end
we’ll move this out into a file:
# heading.ht (partial)
h1 id: id_generator do
text: "Welcome"
end
and then we need to have a helper method which takes a filename and evaluates the contents of the file, adding it to the AST.
class Template < Context
…
def partial(filename)
instance_eval File.read(filename)
end
end
We can then update our template.ht file to call this partial with the header:
partial "header.ht"
p do
text "A Hypertext template."
end
And now, leaving the layout aside for one moment, we have a template which renders a fragment from file in the current context:
params = { page_title: "Hello, World!" }
template = Template.new(params, File.read("template.ht"))
puts template.to_s
# =>
# <h1 id="id-75">
# Welcome
# </h1>
# <p>
# A Hypertext template.
# </p>
This approach to partials feels really clean. We’re essentially applying the same trick for both the template and the partial using instance_eval with the template definition string, loading it from file. This is different to how we put the layout and the template together with two different instances of a Template class and piecing them together via the params hash and append.
In a future post I’d like to explore if we can have “turtles all the way down” and integrate the layout, template and partial using the same technique.
—Monday 5th April 2021.