Interestingly, the best example of an app soliciting user feedback might be the Economist app. Just one alert modal with a simple question — “are you enjoying the Economist app?” — and a simple Yes/No answer. No star rating. No review prose. Just a simple thumbs up/thumbs down. Crude, but effective.

UCL: Brief Integration Update and Modules

A brief update of where I am with UCL and integrating it into Dynamo-browse. I did managed to get it integrated, and it’s now serving as the interpreter of commands entered in during a session.

It works… okay. I decided to avoid all the complexities I mentioned in the last post — all that about continuations, etc. — and simply kept the commands returning tea.Msg values. The original idea was to have the commands return usable values if they were invoked in a non-interactive manner. For example, the table command invoked in an interactive session will bring up the table picker for the user to select the table. But when invoked as part of a call to another command, maybe it would return the current table name as a string, or something.

But I decided to ignore all that and simply kept the commands as they are. Maybe I’ll add support for this in a few commands down the line? We’ll see. I guess it depends on whether it’s necessary.

Which brings me up to why this is only working “okay” at the moment. Some commands return a tea.Msg which ask for some input from the user. The table command is one; another is set-attr, which prompts the user to enter an attribute value. These are implemented as a message which commands the UI to go into an “input mode”, and will invoke a callback on the message when the input is entered.

This is not an issue for single commands, but it becomes one when you start entering multiple commands that prompt for input, such as two set-attr calls:

set-attr this -S ; set-attr that -S

What happens is that two messages to show the prompt are sent, but only one of them is shown to the user, while the other is simply swallowed.

Fixing this would require some re-engineering, either with how the controllers returning these messages work, or the command handlers themselves. I can probably live with this limitation for now — other than this, the UCL integration is working well — but I may need to revisit this down the line.

Modules

As for UCL itself, I’ve started working on the builtins. I’m planning to have a small set of core builtins for the most common stuff, and the rest implemented in the form of “modules”. The idea is that the core will most likely be available all the time, but the modules can be turned on and off by the language embedder based on what they need or are comfortable having.

Each module is namespaces with a prefix, such as os for operating system operations, or fs for file-system operations. I’ve chosen the colon as the namespace separator, mainly so I can reserve the dot for field dereferencing, but also because I think TCL uses the colon as a namespace separator as well (I think I saw it in some sample code). The first implementation of this was simply adding the colon to the list of characters that make up the IDENT token. This broke the parser as the colon is also use as the map key/value separator, and the parser couldn’t resolve maps anymore. I had to extend the “indent” parse rule to support multiple IDENT tokens separated by colons. The module builtins are simply added to the environment with there fully-qualified name, complete prefix and colon, and invoking them with one of these idents will just “flatten” all these colon-separated tokens into a single string. Not sophisticated, but it’ll work for now.

There aren’t many builtins for these modules at the moment: just a few for reading environment variables and getting files as list of strings. Dynamo-browse is already using this in a feature branch, and it’s allows me to finally add a long-standing feature I’ve been meaning to add for a while: automatically enabling read-only mode when accessing DynamoDB tables in production. With modules, this construct looks a little like the following:

if (eq (os:env "ENV") "prod") {
    set-opt ro
}

It would’ve been possible to do this with the scripting language already used by Dynamo-browse. But this is the motivation of integrating UCL: it makes these sorts of constructs much easier to do, almost as one would do writing a shell-script over something in C.

The Perfect Album

The guys on Hemispheric Views have got me blogging once again. The latest episode bought up the topic of the perfect album: an album that you can “just start from beginning, let it run all the way through without skipping songs, without moving around, just front to back, and just sit there and do nothing else and just listen to that whole album”.

Well, having crashed Hemispheric Views once, I’d thought it’s time once again to give my unsolicited opinion on the matter. But first, some comments on some of the suggestions made on the show.

I’ll start with Martin’s suggestion of the Cat Empire. I feel like I should like Cat Empire more than I currently do. I used to know something who was fanatic about them. He shared a few of their songs when we were jamming out — we were in a band together — and on the whole I thought they were pretty good. They’re certainly a talented bunch of individuals. But it’s not a style of music that gels with me. I’m just not a huge fan of scar, which is funny considering the band we were both in was a scar band.

I feel like I haven’t given Radiohead a fair shake. There were many people that approached me and said something of the lines of “you really should try Radiohead; it’s a style of music you may enjoy,” and I never got around to following their advice. I probably should though, I think they may be right. Similarly for Daft Punk, of which I have heard a few tracks of and thought them to be pretty good. I really should give Random Access Memory a listen.

I would certainly agree with Jason’s suggestion of the Dark Side of the Moon. I count myself a Pink Floyd fan, and although I wouldn’t call this my favourite album by them, it’s certainly a good album (if you were to ask, my favourite would probably be either The Wall or Wish You Were Here, plus side B of Metal).

As to what my idea of a perfect album would be, my suggestion is pretty simple: it’s anything by Mike Oldfield.

LOL, just kidding!1 😄

No, I’d say a great example of a perfect album is Jeff Wayne’s musical adaptation of The War Of The Worlds.

The album cover of Jeff Wayne’s Musical Version of The War Of The Worlds

I used to listen to this quite often during my commute, before the pandemic arrived and bought that listen count down to zero. But I’ve picked it back up a few weeks ago and it’s been a constant earworm since. I think it ticks most of the boxes for a perfect album. It’s a narrative set to music, which makes it quite coherent and naturally discourages skipping tracks. The theming around the various elements of the story are really well done: hearing one introduced near the start of the album come back later is always quite a thrill, and you find yourself picking up more of these as you listen to the album multiple times. It’s very much not a recent album but, much like Pink Floyd, there’s a certain timelessness that makes it still a great piece of music even now.

Just don’t listen to the recent remakes.


  1. Although not by much. ↩︎

God bless the person that invented the command line history. They just saved me 15 minutes of work.

And while we’re handing out praises, thank you to the person that added RunAndReturn to the Mockery mock generator. I might be able to climb out of this mocking hell with this before the day is up.

One other thing from Rec Diffs #233: it’s amusing to hear Siracusa being as frustrated with Britishism seeping into American English as I am with Americanisms seeping into Australian English.

John, I know how you feel. 😀

Favourite Comp. Sci. Textbooks

John Siracusa talked about his two favourite textbooks on Rec Diffs #233: Modern Operation Systems, and Computer Networks, both by Andrew S. Tanenbaum. I had those textbooks at uni as well. I still do, actually. They’re fantastic. If I were to recommend something on either subject, it would be those two.

Auto-generated description: Two textbooks titled Modern Operating Systems and Computer Networks by Andrew S. Tanenbaum are placed side by side on a surface.
The two Tanenbaums.

I will add that my favourite textbook I had during my degree was Compilers: Principal, Techniques and Tools by Alfred V. Aho, et al. also known as the “dragon book.” If you’re interested in compiler design in any way, I can definitely recommend this book. It’s a little old, but really, the principals are more or less the same.

Auto-generated description: A book titled Compilers: Principles, Techniques, and Tools by Alfred V. Aho, Ravi Sethi, and Jeffrey D. Ullman, often referred to as the Dragon Book, is lying on a textured surface.
And dragon makes three.

And that makes it the third time this week that I encountered a bug involving DynamoDB that was avoidable with a unit test that actually used a proper database.

Meme of the Simpsons featuring the purple Stern lecture Plumbing van, with the text modified to say 'Stern Lecture Coding' and 'I told you not to Mock that'.

(To be fair, this time is was my fault: I haven’t got around to writing the unit test yet).

Github/Gitlab code search is fine, but have you ever tried grep -l -r methodName projects/*? Seems to be not that much slower and like 100x more reliable.

I wish Ghost allowed readers to choose a different email address to send newsletters, rather than just send them to the email address associated with the account itself. I’ve got news for you: send reading material to my personal inbox and I’ll never see it. That’s just not where I read stuff: it’s all in Feedbin.

Even better would be a private RSS feed. I know Gruber had issues with doing way back during the Google Reader days. But those days are gone, so it might be worth trying this again. Seems to work for Stratechery.

For the last few years, I’ve been using 4/24 as the expiry date of test credit cards within Stripe. Well those days are literally in the past now.

Screenshot of a new credit card setup within Stripe showing the test credit card number of 4242 4242 4242 4242, and the expiry date 4/24, and the error message saying 'Your card's expiry date is in the past'.

UCL: Breaking And Continuation

I’ve started trying to integrate UCL into a second tool: Dynamo Browse. And so far it’s proving to be a little difficult. The problem is that this will be replacing a dumb string splitter, with command handlers that are currently returning a tea.Msg type that change the UI in some way.

UCL builtin handlers return a interface{} result, or an error result, so there’s no reason why this wouldn’t work. But tea.Msg is also an interface{} types, so it will be difficult to tell a UI message apart from a result that’s usable as data.

This is a Dynamo Browse problem, but it’s still a problem I’ll need to solve. It might be that I’ll need to return tea.Cmd types — which are functions returning tea.Msg — and have the UCL caller detect these and dispatch them when they’re returned. That’s a lot of function closures, but it might be the only way around this (well, the alternative is returning an interface type with a method that returns a tea.Msg, but that’ll mean a lot more types than I currently have).

Anyway, more on this in the future I’m sure.

Break, Continue, Return

As for language features, I realised that I never had anything to exit early from a loop or proc. So I added break, continue, and return commands. They’re pretty much what you’d expect, except that break can optionally return a value, which will be used as the resulting value of the foreach loop that contains it:

echo (foreach [5 4 3 2 1] { |n|
  echo $n
  if (eq $n 3) {
    break "abort"
  }
})
--> 5
--> 4
--> 3
--> abort

These are implemented as error types under the hood. For example, break will return an errBreak type, which will flow up the chain until it is handled by the foreach command (continue is also an errBreak with a flag indicating that it’s a continue). Similarly, return will return an errReturn type that is handled by the proc object.

This fits quite naturally with how the scripts are run. All I’m doing is walking the tree, calling each AST node as a separate function call and expecting it to return a result or an error. If an error is return, the function bails, effectively unrolling the stack until the error is handled or it’s returned as part of the call to Eval(). So leveraging this stack unroll process already in place makes sense to me.

I’m not sure if this is considered idiomatic Go. I get the impression that using error types to handle flow control outside of adverse conditions is frowned upon. This reminds me of all the arguments against using expressions for flow control in Java. Those arguments are good ones: following executions between try and catch makes little sense when the flow can be explained more clearly with an if.

But I’m going to defend my use of errors here. Like most Go projects, the code is already littered with all the if err != nil { return err } to exit early when a non-nil error is returned. And since Go developers preach the idea of errors simply being values, why not use errors here to unroll the stack? It’s better than the alternatives: such as detecting a sentinel result type or adding a third return value which will just be yet another if bla { return res } clause.

Continuations

Now, an idea is brewing for a feature I’m calling “continuations” that might be quite difficult to implement. I’d like to provide a way for a user builtin to take a snapshot of the call stack, and resume execution from that point at a later time.

The reason for this is that I’d like all the asynchronous operations to be transparent to the UCL user. Consider a UCL script with a sleep command:

echo "Wait here"
sleep 5
echo "Ok, ready"

sleep could simply be a call to time.Sleep() but say you’re running this as part of an event loop, and you’d prefer to do something like setup a timer instead of blocking the thread. You may want to hide this from the UCL script author, so they don’t need to worry about callbacks.

Ideally, this can be implemented by the builtin using a construct similar to the following:

func sleep(ctx context.Context, arg ucl.CallArgs) (any, error) {
  var secs int
  if err := arg.Bind(&secs); err != nil {
    return err
  }

  // Save the execution stack
  continuation := args.Continuation()

  // Schedule the sleep callback
  go func() {
    <- time.After(secs * time.Seconds)

    // Resume execution later, yielding `secs` as the return value
    // of the `sleep` call. This will run the "ok, ready" echo call
    continuation(ctx, secs)
  })()

  // Halt execution now
  return nil, ucl.ErrHalt
}

The only trouble is, I’ve got no idea how I’m going to do this. As mentioned above, UCL executes the script by walking the parse tree with normal Go function calls. I don’t want to be in a position to create a snapshot of the Go call stack. That a little too low level for what I want to achieve here.

I suppose I could store the visited nodes in a list when the ErrHalt is raised; or maybe replace the Go call stack with an in memory stack, with AST node handlers being pushed and popped as the script runs. But I’m not sure this will work either. It would require a significant amount of reengineering, which I’m sure will be technically interesting, but will take a fair bit of time. And how is this to work if a continuation is made in a builtin that’s being called from another builtin? What should happen if I were to run sleep within a map, for example?

So it might be that I’ll have to use something else here. I could potentially do something using Goroutines: the script is executed on Goroutine and args.Continuation() does something like pauses it on a channel. How that would work with a builtin handler requesting the continuation not being paused themselves I’m not so sure. Maybe the handlers could be dispatched on a separate Goroutine as well?

A simpler approach might be to just offload this to the UCL user, and have them run Eval on a separate Goroutine and simply sleeping the thread. Callbacks that need input from outside could simply be sent using channels passed via the context.Context. At least that’ll lean into Go’s first party support for synchronisation, which is arguably a good thing.

I’d be curious to know why Microsoft renamed Azure Active Directory to “Entra.” That name is… not good.

👨‍💻 New post on Databases over at the Coding Bits blog: Counting In DynamoDB

Day 30: hometown

It’s far from perfect, but it’s good to call this place home. #mbapr

Photo of the Melbourne skyline, facing Flinders St. station and the CBD, with the pedestrian bridge on the right, as taken from a bridge with an iron railing over the Yarra River.

After a two month hiatus, the coffee booth at the station has reopened. All is well in the world once more. ☕😵‍💫

Day 29: drift

Drifted a little from the path at this point of my hike today. Could be easy to get lost though, so it was important not to drift too far. #mbapr

Australian landscape photo of rocks and native plants under a cloudy sky.

📺 Sugar: Season 1 (2024)

Quick review of Sugar: Season 1 (2024), by Mark Protosevich. Review reads as follows: Nah, sorry. I couldn't get through the first episode. I know what they were trying for: classic story of the keen detective, with the fast car and the cool lady companions and all. But it just didn't gel with me (might be because I have no nostalgia for the format). Plus, the cuts across time were awkward: it made it hard to follow what was going on. I'm sure this is for someone, but it's definitely not for me. Overall review: poor

📺 Mission: Impossible – Fallout (2018)

Quick review of Mission: Impossible – Fallout, 2018, by Christopher McQuarrie. Review reads as follows: A pretty competent action movie. Good example of what I'd call an 'airplane movie,' which is a movie that's good to watch on hour 7 of a 14 hour flight. A pretty thin plot that doesn't require a lot of concentration, yet lots of nice set pieces, and some lovely shots of European cities. Overall rating: okay

Day 28: community #mbapr

A local market in front of a collection of national flags from around the world

Manual Moreale hit the nail on the head with this quote from his latest post:

The web is not dying. The web is huge. The web is ever-expanding. The fact that the web is just the same 5 big websites is a fucking lie. It’s like saying the restaurant industry is the same 5 fast food chains. It is not. It’s up to you to decide to stop visiting those 5 sites and stop ingesting their fast food content.

It feels like when these people say “the web”, they mean “whatever platform I’m addicted to.” Might be time they started trying out that URL bar that appears at the top of every browser.