>The error messages and diagnostics emitted by the language are the feedback mechanisms.
The error messages and diagnostics are emitted by the tools like compiler, linker or interpreter and are part of their interface. Language standard may codify some error messages, but language itself cannot present them to you because language is not a program.
>Just because a programming language is all text doesn’t mean that usability metrics don’t exist for it.
Just because some usability metrics can be applied to a programming language, it does not make it UI. Interface implies interaction. You do not interact with language - it cannot receive UI events and react to them, you interact with the tools that understand it.
You’re being overly pedantic to a fault. Here’s the definition Wikipedia gives for UI:
> a user interface (UI) is the space where interactions between humans and machines occur[0]
Further, Wikipedia lists a ton of different kinds of user interfaces. Included among those is:
> Batch interfaces are non-interactive user interfaces
And further, here’s a better explanation describing how a programming language is a user interface then I can provide here[1]. It really is as simple as the programming language being an interface to the machine, and the programmer being the user of that interface. I don’t understand why you’re arguing so much against a widely accepted fact. When computers were first made, there was no such thing as a mouse or keyboard, there were punch cards. The only way for a user to interface with the machine would be to insert a program with punch cards. Nowadays we have all sorts of input devices to give us new ways to interface with machines, but the most basic way we can interface with a machine is by writing a program with our intent for it.
And if you want to be so pedantic then is a pure HTML/CSS website a UI? There’s no program there just markup. The only program that runs is the browser. So then is the website nothing and the browser the only user interface? Or how about the steering and brakes/accelerator in a car? Those are purely mechanical, are they a user interface because they don’t have a program? Or how about the original arcade games like pong? They were directly soldered onto the board. There was no program just a circuit. There were no instructions being executed. So does that make those games a non user interface?
Using labels does not make your arguments any stronger, on the contrary. Speaking of which, you quote Wikipedia, but neither the article you refer to, nor the article "Programming language" does say, that programming language is an interface. Languages by definition are merely syntax and semantics, they are used in interactions but they do not define an interface themselves - it is not an "is", but "is used by" relationship. You can write a program on a sheet of paper and put it in a frame on a wall, so that your friends could read it and enjoy the beauty of the algorithm after a couple of bottles of wine, or you can print it on a t-shirt communicating your identity. In neither case there exists an interaction between a human an a machine.
Interface is always about interaction: a keyboard to write the command or the program on, a display presenting an IDE or command interpreter etc. So, looking at your examples: HTML is not an interface and html file is not, but the static website opened in the browser is, because browser has downloaded the site and now knows how to interface with you. Steering wheel is of course an interface, because, as I said earlier including in my previous comment, it allows interaction. The example with arcade games is actually the same as for the first computer, which did not have an interface for programming (punch cards came later) and had to be re-assembled to run a new program: they did have user interfaces for data inputs and outputs.
Your second reference is clearly written for the beginners and simplifies things to the point where it becomes nonsense, even saying that "Programming, therefore, generally involves reading and editing code in an editor, and repeatedly asking a programming language to read the code to see if there are any errors in it". Do you still think it was worth quoting it?
Now, if you feel that I'm over-pedantic with this response too,
The error messages and diagnostics are emitted by the tools like compiler, linker or interpreter and are part of their interface. Language standard may codify some error messages, but language itself cannot present them to you because language is not a program.
>Just because a programming language is all text doesn’t mean that usability metrics don’t exist for it.
Just because some usability metrics can be applied to a programming language, it does not make it UI. Interface implies interaction. You do not interact with language - it cannot receive UI events and react to them, you interact with the tools that understand it.