[jameshart]

That’s not the claim. It’s well commented and formatted so actually quite readable. The claim is that very few could write it.

Though I would say that ‘very few’ is a larger group than they think - there are plenty of people doing metatype programming in TS; I’ve dabbled enough that given the problem I could probably tackle it and I know I learned from seeing others do it (because I am far from a typescript professional). So it’s not ‘superhuman’ if many of the humans who have found themselves wanting to work with the typescript type derivation model could have written it.

These capabilities - type ternaries and inferred type parameters - were put into TypeScript with a view that humans would use them.

The danger here is kidding yourself that this sort of code is beyond human.

[UncleMeat]

I don't think that this is well commented. It explains what each line does, but it does not explain the overall technique being applied here and what it achieves. "Ah, if the parameter is optional I include undefined" is not useful. Instead what this wants is a block comment at the top explaining what this type achieves, how it should be used, and the strategy employed to construct this type.

[michaelt]

> It’s well commented and formatted so actually quite readable.

Are you looking at the same code I'm looking at? The first block of code from the article?

I've seen more readable code in Perl Golf competitions.

[jameshart]

That’s just how type programming looks.

Here’s (https://github.com/unional/type-plus/blob/main/packages/type...) a human written example that’s well-factored and uses loads of subtypes to clarify what it’s doing - but it’s still going to read like the black tongue of Mordor to you if you’re not familiar with how this kind of type stuff is structured and used.

And factoring all that stuff out may help readability but it doesn’t help comprehension - try and trace what the actual underlying type definitions for some of those utility types like IdentityEqual<> are actually doing (look at https://github.com/unional/type-plus/blob/main/packages/type...) and realize the rabbit hole runs deep in this stuff.

[michaelt]

The fact that unclear code is common does not make it clear.

Single-letter variable names, ternary operators and long run-on lines, like salt, are delicious in small quantities. But when you're writing code so complicated you need multiple comments, within a single statement?

I appreciate that you've got to piss with the cock you've got. I've certainly done things with C++ template metaprogramming, with perl, with TLA+ and with bash that I'm not proud of. But the fact the tool forces me to write something unclear doesn't mean I'm not writing something unclear.

[hwayne]

Can I ask more about the TLA+ spaghetti you had to write?

[michaelt]

In the defence of TLA+ I was a complete newbie.

I mention it only because certain parts of the experience shared the maths-looking big-sequence-of-ands-and-ors one sometimes sees when dealing with complex type systems. TLA+, very sensibly, lets you break up complex statements into multiple smaller statements and give them names.

I was simulating the behaviour of two ends of a communication channel which had been designed with a bidirectional message number/acknowledge/timeout/resend mechanism. And both a hardware and a software state machine on each end managing the message queue in each direction.

The experience was in equal parts brilliant and frustrating. Brilliant because it did reveal faults in the design that probably couldn't have been found any other way. Frustrating because (for example) if you represent your timeout mechanism as a counter on each end of the link and which can only count from 0 to 2 the check will succeed in a few seconds. But if you change the timeout behaviour to count from 0 to 10 the check will take a lot longer. I don't know exactly how long because I aborted the run after a week. And there was no real indication of precisely why it'd stopped completing - I basically had to undo my changes one line at a time until I figured out what was going on.

TLA+ also seemed to have some sort of TeX integration. So a lot of the documentation is written in TeX - it's a fine way of writing math I'm sure. But sometimes the documentation told you how to do something and showed an example statement with a dot, yet you couldn't copy-and-paste the example from the documentation into your code, to express it in your source code you had to use something like \cdot or \circ instead.

Interesting stuff to try out for sure. And impressive given the size of the team that works on it, which I gather is tiny.

[hwayne]

Good to know, thank you. I write a lot of teaching material for TLA+ and this will be helpful to think about.

[yxhuvud]

> That’s just how type programming looks.

Then that is an argument to do less of it. Or at least to back off and learn to write better types that are not a mess.

[awkward]

TS type formatting is an unpleasant language to write in, but it’s touring complete and not that different from C++ type formatting. Writing complex statements in it is just like complex statements in any language - break it down to understandable parts and build those up.