# Literate Ruby (#102)

We definitely have to do more quizzes where the nature of the problem
encourages
submitters to summarize their own solution! Multiple submitters did
just that,
so I recommend taking the time to read through the submission emails if
you

Before we get to the solutions, let me make sure everyone knows about
the
feature similar to this quiz already baked into Ruby. You can often use
the -x
switch to execute code buried inside of normal content, like an email
message.
Here’s an example:

$ruby -x fake_email.txt This is for running Ruby code inside other text! The code is assumed to start at the Shebang line and end at __END__.$ cat fake_email.txt
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do
eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim
ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut
aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit
in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint occaecat cupidatat non proident, sunt in culpa qui
officia deserunt mollit anim id est laborum.

#!/usr/bin/env ruby -w

puts <<END_OUTPUT
This is for running Ruby code inside other text!

The code is assumed to start at the Shebang line and end at __END__.
END_OUTPUT

__END__

Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do
eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim
ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut
aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit
in voluptate velit esse cillum dolore eu fugiat nulla pariatur.
Excepteur sint occaecat cupidatat non proident, sunt in culpa qui
officia deserunt mollit anim id est laborum.


Of course, this is not perfect. It does not handle documents that
slowly build
up code as they discuss it. For that, we will need to go to the
solutions.

The parser for this quiz isn’t overly complex to write. Most people
used a
couple of regular expressions to locate the code. Here is one such
parser from
Cameron Pope:

class LRB
def parse(io)
current_state = :in_text
io.each_line do |line|
if current_state == :in_text
case line
when /^>\s?(.*)/: yield :code, $1 + "\n" if block_given? when /\\begin\{.*\}\s*.*/: current_state = :in_code else yield :text, line if block_given? end else case line when /\\end\{.*\}\s*.*/: current_state = :in_text else yield :code, line if block_given? end end end end end # class LRB  This parser walks the passed IO object line by line. Each line of content is yielded to the provided block along with a type identifier. The parser begins by assuming the content it is reading is :text, and it yields lines with that type. However, if a line begins with the email quote marker (>), that line will be yielded with a :code type. When a LaTeX style marker is found (\begin{code}), the parser switches modes to assume all following lines are now code, until it encounters the matching marker (\end{code}). With a parser in place, the interesting element becomes the supported forms of output. Here are those methods from Cameron’s code: require 'rubygems' require 'bluecloth' class LRB def self.to_code(io) code = String.new LRB.new.parse(io) do |type, line| code << line if type == :code end return code end def self.to_markdown(io) doc = String.new LRB.new.parse(io) do |type, line| case type when :code: doc << " " << line when :text: doc << line end end return doc end def self.to_html(io) markdown = self.to_markdown io doc = BlueCloth::new markdown doc.to_html end end # class LRB  The to_code() method is the most basic. It just uses the parser to walk the document content, accumulating all of the code it finds along the way. In the end, it returns the collected code. The to_markdown() method is similar, but it collects text and code. Text is added normally, but code is indented four spaces to match the rules of Markdown. The resulting Markdown content is returned. From there, to_html() is trivial. The document is converted to Markdown using the method we just examined and then handed off to BlueCloth for translation. The Markdown option is a great fit here, since it was designed with human readability in mind. The whole point of Literate Programming is to write about code, and we obviously want people to read what we write, so that’s a good match. All we have left is Cameron’s interface code: if$0 == __FILE__
opt = ARGV.shift
file = ARGV.shift
case opt
when '-c': puts LRB::to_code(File.new(file))
when '-t': puts LRB::to_markdown(File.new(file))
when '-h': puts LRB::to_html(File.new(file))
when '-e': eval LRB::to_code(File.new(file))
else
usage = <<"ENDING"
Usage:
lrb.rb [option] [file]

Options:
-c: extract code
-t: extract text documentation
-h: extract html documentation
-e: evaluate as Ruby program
ENDING
puts usage
end
end


Here you see a simple set of four supported options. The first three
are the
basic conversions we just examined. The fourth option also pulls the
code, but
it eval()s it, instead of printing the results.

Another step a couple of the solutions took was to enhance require() to
locate
.lrb files. Here’s an example of how this is accomplished, by Vincent
Fourmond:

# Here, we hack our way through require so that we can include
# .lrb files and understand them as literate ruby.
module Kernel
alias :old_kernel_require :require
undef :require
def require(file)
# if file doesn't have an extension, we look for it
# as a .lrb file.
if file =~ /\.[^\/]*$/ old_kernel_require(file) else found = false for path in ($:).map {|x| File.join(x, file + ".lrb") }
found = true
RWeb::run_code(RWeb::unliterate_file(path).first,
self.send(:binding))
break
end
end
old_kernel_require(file) unless found
end
end
end


The comments explain the process pretty well here. The idea is to check
for a
.lrb file in Ruby’s load path, for any require() without an extension.
If such
a file is found, it’s loaded via Vincent’s RWeb Literate Ruby processor.
If not
found or if the file had an extension, is is passed-through to Ruby’s
own

My thanks to all the people who unknowingly helped me design the
quiz/summary
format and parser for Ruby Q. 2.0. As always, the solutions
introduced great
new tricks I never would have thought of.

Tomorrow we will tackle a question commonly asked on Ruby T. in the
hopes that
we can answer if once and for all…

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