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GOTOphobia considered harmful in C

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Re: GOTOphobia considered harmful in C

#181

Post by zozbot234 »

mort96 wrote: post #140
arp242 wrote: post #77

Earlier quoted context omitted.

The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. There's plenty of confusing and messy code around, but true spaghetti code that GOTOs all over the place and is nigh-impossible to follow has been extremely rare for a long time. I can't recall encountering it in the last 30 years. It easy to misunderstand what he was even talking about becau…

To give people some kind of an idea of what it was created in response to: Imagine writing an entire program in one single main function. The only thing you're allowed to do for flow control is goto. You can do 'goto somelabel;' for an unconditional goto, or you can do 'if (somecondition) goto somelabel;' for a conditional goto. Here's some examples of how it would look if if translated to something C-like: Loops wou…

The loop you posted is a do-while loop; the while loop has a somewhat less intuitive translation to GOTO:

  loop_test: IF (NOT loop_condition) GOTO after_loop
    loop_body
    GOTO loop_test
  after_loop: etc...

Re: GOTOphobia considered harmful in C

#182

Post by SOLAR_FIELDS »

eric__cartman wrote: post #147
saagarjha wrote: post #142

Earlier quoted context omitted.

If it was created today? I’d go for Rust and Python respectively

The ATmega 328P an Arduino Uno or Nano uses has 2KB of memory and 32KB of flash storage for the program. Having some sort of micropython interpreter there would be impossible, and even if it could be achieved, somone still has to write the low level C/ASM code to make it all work. For many embedded systems, low level languages like C or C++ (perhaps Rust for a lot of ARM micros) is the only sensible choice. If it's n…

I hope Rust takes off for embedded programming. I've been working with ESP32 and C is really the only choice if you are doing anything remotely fancy or resource constrained

Re: GOTOphobia considered harmful in C

#183

Post by erik_seaberg »

edflsafoiewq wrote: post #165
erik_seaberg wrote: post #159

Earlier quoted context omitted.

This has been called the https://en.wikipedia.org/wiki/Rule_of_least_power , and it’s a good way to make legible what you’re doing and especially to exclude what you aren’t doing.

The problem with this is it requires introducing a vast zoo of features distributed across the spectrum of power, and it is not at clear that it is actually easier to learn this whole zoo so you can select precisely the least powerful point on it, than it is to understand the use of a single (or small number of) all-powerful constructs within its context.

My goal is “most reliable and concise for experts,” because we should spend most of our careers as experts, and “easy to learn” requires bad tradeoffs too often. Learning common names and reusing tested implementations pays off over rolling my own on the spot and forcing everyone else to re-read it.

Re: GOTOphobia considered harmful in C

#184

Post by version_five »

pavlov wrote: post #86
arp242 wrote: post #77

Earlier quoted context omitted.

The thing is that many people today have never encountered the sort of spaghetti code that Dijkstra was talking about in 1968. There's plenty of confusing and messy code around, but true spaghetti code that GOTOs all over the place and is nigh-impossible to follow has been extremely rare for a long time. I can't recall encountering it in the last 30 years. It easy to misunderstand what he was even talking about becau…

This. To find an example, I did a search for “Commodore PET Basic programs”. Here’s a book from 1979 that shows what spaghetti code looks like, in my opinion: http://www.1000bit.it/support/manuali/commodore/32_BASIC_Pro... The first program listing is on page 24 of the PDF. Try to follow the logic of the program. Why does line 400 go to 280? What paths can lead to line 400? Who knows! And this is high-quality BASIC b…

Pretty sure we had that program on our home computer in the 80s (I was a young kid but I distinctly remember a biorhythms program). What impresses me reading it now is the "y2k" compliance. If the year entered is only two digits, it adds 1900, otherwise it takes the full year.

Re: GOTOphobia considered harmful in C

#185

Post by bee_rider »

spacechild1 wrote: post #173
bee_rider wrote: post #148

Earlier quoted context omitted.

Those are just regular loops, though, right? I’m looking for the posttest loop, sometimes known as the do…while or until loop. There seems to be a unfortunate inconsistency in the naming of this thing.

Ah, right, I misread your post. DO WHILE is indeed a "normal" while loop. There doesn't seem to be an equivalent to "do { ... } while", as found in most C-style languages. > There seems to be a unfortunate inconsistency in the naming of this thing. Well, Fortran is older than C, so you cannot really blame them :-)

The funny thing is, I mostly program in Fortran (thus the interest in this construct). It is nice for expressing “this iterative method must be run at least once.” Unfortunately at some point I absorbed the name that comes from the C-ism, haha.

Re: GOTOphobia considered harmful in C

#186

Post by throwaway2037 »

cesarb wrote: post #161
kentonv wrote: post #66

Earlier quoted context omitted.

IMO this is a design bug in C++. The authors couldn't agree on what to do in the exception-during-unwind scenario, so they chose the worst possible option: crash. In most cases, an second exception raised while another exception is already being thrown is merely a side-effect of the first exception, and can probably safely be ignored. If the idea of throwing away a secondary exception makes you uncomfortable, then an…

> If the idea of throwing away a secondary exception makes you uncomfortable, then another possible solution might have been to allow secondary exceptions to be "attached" to the primary exception, like `std::exception::secondary()` could return an array of secondary exceptions that were caught. Java has that for its pseudo-RAII "try-with-resources" statement: when an exception happens during cleanup of a try-with-re…

I agree with your points about Java. I have direct experience with suppressed exceptions in Java 6 -- it was painful to debug ("where did my exception go???"). However, this works because Java forces everything thrown to be a sub-class of Throwable. (Please correct me if wrong.) C++ allows you to throw anything, including (bizarrely) null. I learned recently that C# allows the same -- you can throw null(!). How does C# handle suppressed exceptions?

Re: GOTOphobia considered harmful in C

#187

Post by Gibbon1 »

bazoom42 wrote: post #122
lolinder wrote: post #118

Earlier quoted context omitted.

CONTINUE and BREAK are quite different from GOTO in that they operate predictably given the current scope: their limitations make them incapable of creating the unstructured nightmare that Dijkstra was talking about. They're similar to a GOTO only in that they compile to a jump, but so do IF statements and FOR loops. Structured programming wasn't about eliminating jumps, it was about enforcing discipline in their use…

The argument against gotos in Dijkstras article would apply equally to breaks and continue and even to early returns. I dont fully agree with Dijkstras argument. For example I think early returns can often improve the readability of the code. But worth noting Dijkstra is not primarily concerned about readability but rather about how to analyze the execution of a program.

Far as I could tell coming in on the end of it people like Dijkstra were primary trying to write proofs about programs. That motivated them to ban constructs they didn't know how to analyze. Problem is that some of those things turned out to be trivially tractable but lots of people never got the memo.

Re: GOTOphobia considered harmful in C

#188

Post by Gibbon1 »

codebje wrote: post #145
Someone wrote: post #103

Earlier quoted context omitted.

> And this is high-quality BASIC by 1979 standards — it’s in a printed book after all. I don’t think that’s true, certainly not for books of that time period. Because the whole field was changing rapidly, writers would often work under tight schedules, and customers would buy about anything because they only had magazines and books to learn from and review sites didn’t exist. I also think that’s bad Basic for the tim…

It looks pretty typical for BASIC of the late 70s to me. You wouldn't want to waste characters on commenting code: machines of that era would have only a few KB of RAM, as low as 1K. For the same reason you don't want to waste characters on long, meaningful variable names or on well spaced code. Multiple statements per line isn't to save print space, it's to save RAM. Meanwhile, the program's pretty well structured f…

I messed with some programs written in basic for industrial controllers that was written in late 1970's.

There is a simple thing. On a lot of machines only spaghettified programs would even fit in the memory available. Academic CS researchers with their unlimited accounts on the institutions mainframe didn't have that worry.

Re: GOTOphobia considered harmful in C

#189

Post by Jtsummers »

Gibbon1 wrote: post #187
bazoom42 wrote: post #122

Earlier quoted context omitted.

The argument against gotos in Dijkstras article would apply equally to breaks and continue and even to early returns. I dont fully agree with Dijkstras argument. For example I think early returns can often improve the readability of the code. But worth noting Dijkstra is not primarily concerned about readability but rather about how to analyze the execution of a program.

Far as I could tell coming in on the end of it people like Dijkstra were primary trying to write proofs about programs. That motivated them to ban constructs they didn't know how to analyze. Problem is that some of those things turned out to be trivially tractable but lots of people never got the memo.

If you read Dijkstra's letter it wasn't about formal proofs. It was about go to statements being very hard to reason about, especially when trying to understand the flow of a program and how you got to a particular point in its execution. The word "proof" doesn't even show up in the letter. It's only a page or so, well worth a read instead of guessing at what he may have been writing about.

http://www.u.arizona.edu/~rubinson/copyright_violations/Go_T...

Re: GOTOphobia considered harmful in C

#190

Post by lmm »

eric__cartman wrote: post #147
saagarjha wrote: post #142

Earlier quoted context omitted.

If it was created today? I’d go for Rust and Python respectively

The ATmega 328P an Arduino Uno or Nano uses has 2KB of memory and 32KB of flash storage for the program. Having some sort of micropython interpreter there would be impossible, and even if it could be achieved, somone still has to write the low level C/ASM code to make it all work. For many embedded systems, low level languages like C or C++ (perhaps Rust for a lot of ARM micros) is the only sensible choice. If it's n…

> The ATmega 328P an Arduino Uno or Nano uses has 2KB of memory and 32KB of flash storage for the program.

And costs the same as an ARM with dozens of megabytes of each.

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