I Wrote a Software: My Tech Stack

I’ve been writing recently about a side-project of mine that I’ve been doing to scratch a couple of itches I have: Using Excel as a Collaboration Tool in an Enterprise Setting and Seeing what all the fuss is about Haskell.

I started off, reasonably enough, by trying to write a web app. But getting started with anything in Haskell is hard enough: getting started with a website was a nightmare [1]. So I made a virtue of necessity. I figured if I’m going to make it easier for people to collaborate with Excel then what is the most natural way for people to collaborate with Excel in real life? The answer is simple: by sending email attachments.

So I forgot about any web interface (for now) and just concentrated on working with Excel Attachments on Emails. It meant I could just focus on learning Haskell and also forced me to work in a way that is going to be more natural for anyone who might use the service. And also it turns out that I’m bang on trend with this whole “No UI” movement [2].

In this post I’m going to get into what I’m using on this project and why:

  1. Ubuntu. I run this on the server simply because I’m used to using Ubuntu on the desktop from the past. I’ve run Ubuntu in production for a long time and it’s fine for me. (I’ve also run CentOS and Windows and going back far enough HP-UX and Solaris, but Ubuntu just seems… nice).
  2. Linode. Not all that much thought on this one. I’ve used AWS in the past and find the interface unbearably complex. I’ve used Rackspace Cloud with a lot of success. But I’ve also been curious as to how Linode and Digital Ocean stack up. I asked Twitter and I got an answer from someone in the Linode community. And so here I am.
  3. Postfix/Dovecot. I never imagined running my own mail server. I originally wanted to run all the email through Gmail. But I kept getting blocked for having a script running against the Gmail servers. In the end I figured I may as well run my own. Remains to be seen how well that works out. And (perhaps coincidentally) the best guide I could find to setting up Postfix/Dovecot was from Linode.
  4. MongoDB. I know that Mongo is no longer the cool kid on the block. But given that my use case for data storage is pretty straightforward, but I expect to need to store large Excel files, Mongo seemed neat. I’m using Mongo as a queueing system as much as a persistent data store.
  5. Haskell. For the heavy lifting. Learning it has been a long, hard slog. I must have read Learn You a Haskell 15 times (I even bought a copy). And also Real World Haskell several times. But you only really learn by doing and for me the best doing came from trying to follow Write Yourself a Scheme and then by trying to figure out how the HaExcel guys did it. Hat tips must also go to HaskellLive for getting an environment set up (though this now seems to be superseded by Stephen Diehl’s excellent write-up).
  6. Plain vanilla Ruby. Because with the wealth of gems in the community you can do a lot very easily.

[1] My brother who also works in tech bought me a copy of Building Web Applications with Haskell and Yesod. He thought that Haskell and Yesod were two individuals who were doing the teaching. This is in stark contrast to Ruby which I learnt from Alan Bradburne’s excellent Practical Rails Social Networking Sites.

[2] A cynic may say that mailing lists have been doing this for donkeys years. To which my reply is that the surely this validates the use of email for sending instructions around.

I Wrote a Software Part III: A Solution

In parts 1 and 2 I outlined the challenges I see on a daily basis with people trying to collaborate with Excel and how I’ve written some software with a view to improving things a bit.

Here is what I have working right now. You send an email with two Excel files attached that people have been working on and you get emailed back to you a result that could be:

  • The differences between the files
  • The two files merged together
  • The two files stitched together

It works with XLSX or XLSM files.


If you send two files to “diffs” it will send you a file showing the differences between two Excels


If you send two files to “merges” then it will combine the cell values from the second spreadsheet into the first spreadsheet. This is useful where you have for example one excel with loads of questions in and you have different people answering different questions within the one excel. You can use this tool to merge together all their changes.

  • In the body of the email you should include one line that says Concat or Replace. Concat will concatenate (join together) the values in two differing cells. Replace will replace the value in the first sheet with any different values from the second sheet. (Any values that are present only in the first sheet will be untouched).
  • In the body of the email you can also include one line with a cell reference in e.g. Sheet1!A6. If you include this then the style of that cell will be used to colour code any changes that were made.


If you send to “stitches” then the system will take new rows from the second sheet and stitch them to the bottom of the first sheet. This is useful if you have a spreadsheet with a different company on each row and you have different people contacting different companies for updates. Any information in additional columns will get stitched into a sensible place.

What about future plans?

I have some thoughts around an opinionated way of enabling collaboration across different Excel users using what I’ve called XF functions. Essentially these are special functions that are processed on the server side based on the values in a range of other spreadsheets. Watch this space for more updates on these features.

Assuming there is sufficient interest then the commercial model will be based on a monthly subscription which allows you a certain number of credits per month. A diff costs 1 credit, merges and stitches cost more.

I’m opening this up as an alpha right now so if you would like to give it a go please mail alpha at elevenfortyfive dot com and I will add you.