Functional Programming Talks

In the past few months the following lectures have greatly helped my understanding of how algebraic structures can be used to design and construct functional programs:

• Parallel and Concurrent Programming in Haskell by Bartosz Milewski
• Denotational Design: From Meanings to Programs by Conal Elliot

Update on Sun 2017-01-22 by Tristram Brelstaff

I should also add the following lectures which I am currently working my way through:

• Category Theory by Bartosz Milewski

Update on Sat 2017-02-11 by Tristram Brelstaff

And for a mathematician's take on category theory you should really watch:

• Category Theory by Tom LaGatta

Tim Bray on Javascript

JavaScript is horrible.

> [5, 10, 1].sort();
[ 1, 10, 5]

Et cetera.

From here

RVM SSL Certificate Errors

The Ruby Version Manager RVM is one of the key components in a Ruby development environment on non-Windows platforms.

Yesterday I wanted to install it on my Ubuntu laptop.  The recommended way of doing is to run the following command in a terminal:

curl -L https://get.rvm.io | bash -s stable

Unfortunately this gave SSL certificate verification errors.  Visiting rvm.io in Firefox and Chrome indicated that this was due to the site's security certificate having expired.

A little Googling revealed the recommended workaround which is to use Gihub instead of rvm.io:

curl -L https://raw.github.com/wayneeseguin/rvm/master/binscripts/rvm-installer | bash -s stable

Misleading minus signs in Cucumber progress format

I have been recently using the Ruby test tool Cucumber and came across a little annoyance.  In the progress format output there were unexpected minus signs:

  $ cucumber --format progress features/codebreaker_submits_guess.feature
  ---..........................................
  14 scenarios (14 passed) 42 steps (42 passed)
  0m0.117s 
  $

Normally minus signs would be used to indicate skipped steps but here they seem to be displayed for each scenario outline step whether it is skipped or not.

A little Googling revealed that this is a known bug that has not yet been fixed because of the awkward internal design of Cucumber.

How to Inhibit Escaping in Rails3 ActionView Custom Helpers

I had bits of code like this scattered throughout my Rails3 views:

  <%= image_tag(thumbnail_image_path(@image.id)) %>

I wanted to enclose each image_tag call in a <div></div> pair to allow styling, so I wrote the following custom helper and placed it in app/helpers/application_helpers.rb:

  def thumbnail_block(image_id)
    "<div>#{image_tag(thumbnail_image_path(image_id))}</div>"
  end

I then replaced the calls to image_tag in my views with calls to thumbnail_block:

  <%= thumbnail_block(@image.id) %>

However, instead of displaying the images, this displayed the HTML code in the browser window.  Rails3 was automatically escaping the string produced by the new custom helper.

A search on Google lead me to this answer by Mike Fisher at StackOverflow and this post by Yehuda Katz at Rails Dispatch.  These gave me the solution: the custom helper needs to mark the string as html_safe before returning it:

  def thumbnail_block(image_id)
    "<div>#{image_tag(thumbnail_image_path(image_id))}</div>".html_safe
  end

Now my images display properly.