What Is Type-Level Programming?

Post by mrkeen » Wed, May 03, 2023, 12:40 PM UTC

sondr3 wrote: post #54

mrkeen wrote: post #51

The author didn't show any type-level programming here. The author called into library which may or may not use type-level programming. Pin doesn't have set_high() ? I don't see any type-level stuff here. If it had been: Pin on the other hand...

There's a small difference between type-level programming and type-driven programming, Idris does the latter while Rust the former (at least in my opinion). The library uses types to make illegal states impossible and therefore should qualify as type-level programming.

Post by pjmlp » Wed, May 03, 2023, 1:44 PM UTC

efnx wrote: post #35

actionfromafar wrote: post #7

Earlier quoted context omitted.

Ok, that was harsh, but I was excited and wanted to get to the meat of the article but then it just ended. I was thinking, "that's not how I would design a C++ interface". I still don't understand what these Rust types are good for, but I want to know. I miss how in Ada you can define which values an int can have. Can you do that in Rust?

You can do with a sum type (enum) that is represented by a u32 (repr(u32)), or converts into one. Though I don’t know Ada so can’t speak to how accurately I’m creating the analogy.

    type
      Subrange = 56..100;
      Colors = (Red, Green, Blue);
      Pixel = array [Colors] of byte; 

Post by pjmlp » Wed, May 03, 2023, 1:50 PM UTC

tialaramex wrote: post #63

pjmlp wrote: post #26

Earlier quoted context omitted.

Yeah, but then the example is anyway flawed, type level programming is also a thing in C++.

C++ inherits from C the flaw that it is as Dennis Ritchie put it "Strongly typed but weakly checked". In this case that hurts really badly because it means your C++ compiler is likely to let you do stuff that's nonsense, because checking isn't part of the job description, if you claim this Duck is a Goose the C++ compiler just rolls its eyes, sure whatever, however rustc says that is a Duck, you said it's a Goose but…

Post by shakow » Wed, May 03, 2023, 2:40 PM UTC

pjmlp wrote: post #65

shakow wrote: post #50

Earlier quoted context omitted.

And maybe, just maybe, the guys knows Rust better than C++ and just want to take an example from their daily work rather than take every single precaution not to hurt the fragile sensibilities of HN reader unable to see the point if their life depended on it?

Then they should have presented the case that way, instead of showing C like code and assuming there is no way to do that in C++.

Post by sophacles » Wed, May 03, 2023, 2:56 PM UTC

IshKebab wrote: post #67

sophacles wrote: post #61

Earlier quoted context omitted.

> Yeah, and it's trivial in C++, what's your point? I see lots of assertions of that fact, but no examples. Care to link some actual code? > Why the hell would you want to change the direction of a pin anyway? Just declare it as Pin or Pin . i2c uses the same pin for sending and receiving and changes the mode of the pin for the purposes of communication with peripherals.

Ignoring the fact that nobody is bit bashing I2C (there are other protocols that you would bit bash), you don't normally change the mode in that case either. You set it to an output with drive-low and float-high. It's essentially an InputOutput mode.