Learning Haskell gave me a whole new outlook on programming

A while back I decided to learn Haskell as a counterpoint to Ruby/Java etc that I was more familiar with previously. I am very grateful for the new perspective that learning Haskell has given me. In particular:

  • I always used to start with database tables and a user interface. Haskell forces you to think about the functions and how they work on data structures. Not having to think about data storage is strangely liberating as it is much easier to change your data structures if there is no UI or database to worry about.
  • It might need a lot more thinking to write a piece of code, but by the time you’ve finished it invariably feels very elegant.
  • Writing pure code and then wrapping IO around it later really forces you to write code that is simpler and more testable.
  • I have an appreciation of how intimidating jargon can confuse and put people off, unnecessarily. For example, Haskell purists might want you to grok Category Theory even if it’s not that relevant to writing Haskell apps.

The learning curve has been ridiculous. Have a look at Tymon Tobolski’s comparison of using Ruby vs Haskell in a small Redis application. The Haskell version is terse to the point of being incomprehensible at the outset. As a Haskell learner I couldn’t find something that packed a similar “wow” to “A blog in 15 minutes with Ruby on Rails”

Here’s a small Scotty/Warp Haskell app I put together recently. (Scotty is Haskell’s answer to Sinatra for you Rubyists).

Impress your CTO – Track Everything

The day after your new feature goes live, someone will want to know how well it’s working (or not). They don’t just mean “are there any exceptions in the logs”. They mean “how are people using it, if at all?”

Hopefully, you had thought about unspecified requirements and so you already implemented something that they can see. It doesn’t even have to be super heavyweight. I’ve seen good stuff done using something sophisticated like Heap Analytics, and also seen people be able to get actionable insights from something as simple as Google Analytics.

Whatever you choose to do, make sure that there is an easy way for a non-developer to dig around the stats, and ideally download some raw data to play around with offline.

Just be sure to track everything.


Impress your CTO – avoid these boring complaints

Here are some of the most boring complaints I hear.

  • No-one knows how it works
  • You can’t measure the quality of what I’m doing
  • It’s because of all of our technical debt
  • We need to re-write this from scratch

They each contain an element of truth but at the same time they manage to completely miss the point. Hence boring.

No-one knows how it works

This really means “I don’t know how it works and nor does the person I usually work closest with”. I once saw a developer spend a huge amount of time trying to recreate, by reading the friendly source, the possible state transitions for a particularly key entity. Because “no-one understood it”. This had two problems:

  1. He may have missed something
  2. By reverse engineering requirements from the working code, what he ended up describing might have included bugs rather than how the feature was supposed to work.

And in this particular instance I could have pointed the developer to one person still in the business and one person who had left but would still be helpful. Next time you’re tempted to assert “no-one understands these state transitions” just change it to a question: “Is there anyone either on the team here, or who has left but is still friendly, who can help me understand how these state transitions are supposed to work?”

You can’t measure the quality of what I’m doing

This is invariably an attempt to hide something. I once worked with a team who didn’t report their test coverage because the lead developer felt that software is too complicated for a metric as simple as test coverage to be meaningful. We debated the subject and eventually agreed that although 100% coverage is probably not that meaningful, it is worth at least knowing where you are. Where were they when they measured code coverage? About 15%. I was amazed. Here we were debating the costs and benefits of 90% or 100% code coverage and all the time we were staring 15% in the face. I cannot think of anyone who would seriously argue that code coverage of 15% is in any way acceptable. For sure, you can’t measure everything, but the skill of a good developer is in helping finding a useful metric to use. For example on a recent project we agreed on a simple metric that if RubyCritic gives us an  A or a B grade then that’s good, if it’s any worse then we need to know why. It’s not perfect but it’s a lot better than hiding behind “you can’t measure what I’m doing”.

It’s because of all of our technical debt

As an experiment, I once agreed with a team to spend one month just doing technical debt cleanup. The results? Nothing noticeably better or faster for the users, nothing notably better quality as far as the QA people were concerned, no metric to show anything had improved, and I was still getting the same developers 3 months later making the same complaints about technical debt. The reality is that there will always be technical debt of some shape or form. Just like real world debt, some technical debt can be good if it helps you achieve other ends that you couldn’t otherwise achieve. Better developers would have a plan that says, for example, “Technical debt in module X is causing us problems, in order to fix those we will need to do Y”. This is better because it is specific and measurable and, if defined well enough, deliverable.

We need to re-write this from scratch

Stop thinking that. It’s a dreadful idea. Whenever you think of re-writing you are thinking of the 20% of the system that is a PITA to maintain. You’re not thinking of the 80% of the system that you will also need to re-write. I remember one project where a 5-month re-write was still going on 18 months later, still with no end in sight. And another where a re-architected system was being built in parallel but wasn’t able to keep up with the new features being added to the “legacy” platform. In shoert I’ve never seen a complete re-write that people were glad to have done. If you do need to make dramatic changes then you will need to find some way to change very specific parts of the application one by one. It will take a very long time: make sure you do your homework before advocating this.

Impress your CTO – Define your own NFRs

In the last instalment I talked about unspecified requirements. These are the ones that your product owner takes for granted: Of course the system should export to Excel; of course it should authenticate with Facebook; of course the system should load pages blazingly fast irrespective of how much data is thrown at it.

The most common of these unspecified requirements are the Non-Functional Requirements (NFRs). And the most common of these NFRs is “how long should the response time be”. So I find it surprising that response times are very rarely (if ever) mentioned during requirements definition work. Avoiding the topic early in the project is a sure way to have problems later on in the lifecycle.

It’s not uncommon to experience a conversation like this:

Sales: “This software is dreadful, it just took forever to load the dashboard in a crucial demo”
Dev: “Let’s see what’s up… oh yes you created a wizzabanga with 38 different permutations”
Sales: “Well yes of course I did. Then it took forever to load into the dashboard. Your software sucks.”
Dev: “But we didn’t have any NFRs”
Sales: “What’s an NFR”
… some tedious conversation ommitted ….
Dev: “So give me an NFR”
Sales: “OK, I want the page to load up in 200ms even if I’ve got 1000 wizzabangas each with 100 permutations”
Dev: “Hmmm… going to cost you”


It’s meaningless to ask your user base for open-ended NFRs. Clearly they want everything to be really fast and really easy and really secure and ready next week. Much more useful would be for you to set out some reasonable NFRs that you think are deliverable in a reasonable timeframe and, even impose some sensible limits or warnings in the system to ensure those NFRs are supportable. Then at least you have an NFR, even if it’s one that you created.

For example if you think it’s reasonable for the page to load “fast enough” if your wizzabanga have up to 10 permutations then either impose a limit in the UI, or even just a sensible warning, “e.g. we recommend that you have no more than 10 permutations in your wizzabanga. You can add more but please note that you will need to be patient when loading larger wizzabangas.”

Impress your CTO (3)

Imagine the following conversation between a product owner and developer

Product Owner: “I want a CRM system”
Developer: “What does that do?”
PO: “It’s a customer database that lets me manage and report on my communications with my customers”
Dev: “That sounds easy, I’ll build you one this iteration”

One week later …

Dev: “Here you go. You log in here and here’s a screen where you can add a record for each customer. When you click into a customer record you can also add some notes for each time you’ve talked to them”
PO: “Wow, you did all that in a week, awesome. Now let’s add in the ability to make some notes for future calls that I need to do and a screen to show what tasks I have upcoming”
Dev: “No problem”

One week later …
PO: “This is so cool”

Brand new projects often start like this. But it doesn’t take long for fatigue to kick in. A few more iterations and all of a sudden you’re getting bogged down in details like:

  • Download to Excel
  • Upload from Excel
  • The fact that you should really be validating postcodes
  • And show the location on a map
  • And have better collaboration facilities
  • And handle customer segmentation
  • Ability to handle email templates
  • And initiate voice calls
  • And route incoming calls to an appropriate agent
  • And let someone apply a credit to a customer’s account
  • etc, etc, etc

At this point you start to realise why no-one sane would build their own CRM.

The Importance of Unspecified Requirements

You see you have functional requirements and you have non-functional requirements. But beyond all of these you have the unspecified requirements. These last ones are really important because your product owner considers them so obvious that they aren’t worth mentioning. Of course your CRM system has to handle loading records from Excel – only a buffoon would not know that!

The solution isn’t to insist on 100% detailed specifications before you start building. That way another type of madness lies. Nor should you consider your job well done because each week you have built what your customer asked for. The best developers are the ones who deliver the best working software, which is not as simple as building what was written down in the spec.

Worry about their unspecified requirements before you get too far down any path. It doesn’t have to involve much coding (if any). If someone asks you to build a CRM then do a sort of throwaway prototype first. Not one that involves any coding. (I’ve seen some great throwaway prototypes written using Excel). Why not get a one-month license to Salesforce (or whatever). This is a great way to get to see really what features they value, where their frustrations are etc. Then if you discover that Salesforce is the right answer for them then thank your lucky stars that you’ve had a narrow escape from attaching a massive bespoke millstone round your neck for the rest of the time with your company. And if you discover that there is something really special about your requirements, well, then you can build a truly great application that really addresses the real problems your users are facing.


Impress Your CTO (2)

People expect software to “just work”. You can guarantee that it won’t
“just work” when someone decides to throw more data at than you expected. So my 2nd tip is:

Enforce Sane Limits

From a developer point of view it makes sense to think in terms of 1 to Many or Many to 1. Why put in extra work to enforce some limitation when you can have unlimited flexibility for free?

Because the real world doesn’t work that way and it’s more important to model the real world than it is to create infinite flexibility. Some good reasons:

  1. Usability
  2. Performance
  3. Commercial reasons


The more “many’s” in your one to many, the more UI real estate you need to think about. Pagination, sorting, searching, exporting lists to Excel. Maybe favouriting so that people can shortlist the results because they can’t make sense of the whole list. Nothing here is super-complicated to code, but given that the scarce resource in most tech operations is developer time, as a great developer you will be ensuring that you are spending your valuable time on the most value-add activities.


Be honest. You aren’t about to write comprehensive automated performance tests. If you allow people to add unlimited items then eventually someone will do so and, probably sooner than you expect, you will experience serious performance issues. Which then means that you need to be spending valuable developer time addressing those performance issues because by the time you have enough traction to have performance issues you aren’t going to be able to withdraw the poorly performing feature [*].

Commercial Reasons

Maybe a surprise to see this as a reason but it may be the one you would do best to remember. The simple point here is that if the standard version of your product allows the user to add up to 15 items to a Thingamy then not only do you lower the risk of performance issues etc but you have a built-in mechanism that your product managers can use to upsell your customers to the next subscription level: “You want to handle more than 15 items? Let me put you through to our Enterprise Sales team”. If there is demand for the feature and customers will pay for it then fantastic – it will be a great feature to spend some real effort and attention to and give it a stunning user experience that performs really well.


I’m not saying to do anything complicated in your database. Leave the database handling a 1 to Many relationship. Just put check somewhere in your business logic. Next time you are discussing a feature with your product owner and you are thinking about the many side of the object model, just ask the question: “Would 5 be enough?”

[*] This is a case of “do as I say, not as I do” here. In my own side project which allows a user to merge and stitch together data from different Excel files I didn’t impose any limits. I asked some friends and family to test it and the second thing my brother did was try to crash it. It worked. So now I’ve implemented some limit checking.

Impress Your CTO (1)

There are plenty of developers who will happily build the functionality described in a set of requirements.

That is fine as far as it goes. We need requirements and we need to deliver working software to satisfy requirements. But it takes a LOT more than just this to build decent software products. Not only are there a myriad different ways to satisfy a set of requirements, but even more exciting, in today’s agile (small a) world developers have a great opportunity to co-create products with their product owners.  And in the process to become great developers, not just good developers.

So I want to share some personal views on what you should be thinking of to become a great developer. I’m taking for granted that you know your framework, you know how to use Stack Overflow and that you write good unit tests. I’m going to be talking about the other stuff. The stuff that, in my view, distinguishes great developers from, well, just developers. The stuff that, when I see it in my team, helps me sleep more soundly, knowing that the codebase is in good hands.

Here’s the first one.

Learn your database

Your framework is great. It has a lot of really cool abstractions so you can program away without having to (amongst others) handle all the tedious details of writing SQL [1].

Time for a story.

A product owner was launching a new product and wanted to give the impression that it had been around for a long while. A reasonable request, I mean, who wants to know they are being billed with Invoice #1. The solution was to use a higher number. So the first invoice would be #225678 rather than 1, for example.

This is trivial to do with any RDBMS I’ve seen: you just set the auto-increment to the appropriate number, rather than start counting from 1.

Not in this case. The developer didn’t want to get involved in proprietary database commands. He decided to use a parameter, let’s call it INVOICE_OFFSET, to adjust what someone would see on the UI. Sounds simple enough – set INVOICE_OFFSET to 225677 and every time you show an invoice number on the UI or in an email add INVOICE_OFFSET to the database id. Likewise, subtract before you do any CRUD operations on the database.

Can you see where this is going?

It was fine while there was only one developer involved in the product. It soon turned into a bit of a mess when new developers came on board and weren’t expecting this INVOICE_OFFSET idea. For example in a REST situation, would you use the database ID in the URL? Or use the ID that the user would recognise? And then when you were interpreting the ID in the URL, is it a database ID or an adjusted ID?

True story [2].

I fully accept that writing SQL by hand is horrible and so I am very grateful for ORMs for abstracting that away. But too many developers have gone too far the other way and treat the database as a black box. Or go as far as learning about indexes.

Databases are pretty awesome pieces of software, see what else they can do to help you build better applications.


[1] Hell, you could even write an application that you can then easily port from one database to another should you want to. Though if there ever was a case of YAGNI, having an app that you can port between databases should be a top contender.
[2] To be fair, I don’t think there was ever a production issue where one person could inadvertently see someone else’s invoices, but it was certainly a PITA during QA time.