Flowcharts of programming language constructs

https://www.progsbase.com/blog/flow-charts-of-programming-language-constructs/

253 84 6 years ago

zabzonk2• 6 years ago

A brilliant explanation of why no-one uses flowcharts.

notacoward4• 6 years ago

...because if they did, they might realize that some of their favorite structures are a hot mess. Seeing things in a new way often leads to learning, which a good developer would welcome. Personally I can't remember the last time I used an actual flowchart, but I do use state machines. Sometimes I'll go through an exercise of re-casting complex logic as a state machine. Often, that leads to a realization that making the state machine explicit would yield far more testable and maintainable code than leaving it in its more common if/loop/nested-function form.

whatshisface• 6 years ago

they might realize that some of their favorite structures are a hot mess

Normal brain: Find the representation that best expresses the structure to discover the hidden simplicity in everything.

Galaxy brain: Use flowcharts to draw out how exceptions work, forget your previous understanding, and then realize that they are too complicated for anyone to use.

gnulinux• 6 years ago

Exceptions are rather easy to reason in the code but their flow chart looks like a hot mess. So your argument is invalid?

AnimalMuppet6• 6 years ago

...because if they did, they might realize that some of their favorite structures are a hot mess.

They may only be a hot mess when expressed as a flowchart. But so what? I'm not programming in flowcharts. If exceptions can do what I want cleanly, why do I care if it's a mess considered as a flowchart? That's not my problem.

This argument is like saying that the library function I call is a mess of a flowchart. Why should I care? Can I express what I need to express cleanly by calling that function, or not?

Of all the arguments against exceptions, "it's got a mess of a flowchart" is the absolutely least relevant one.

gugagore• 6 years ago

I strongly agree that multiple ways to look at things is good.

Programming languages have different "things" built in. Like, if you have re-entrant function calls, then your language has a built-in data structure called "the stack". If you have some algorithm that needs a stack, you have the choice of using the built-in stack, or using an explicit stack.

If you have a programming language with some sort of type system, then you have tagged data built-in. You can model your domain in the type system, or you can model your domain using a tuple like (tag, datablob).

If you have object-oriented programming with dynamic (single) dispatch on the first argument, then your language somewhere has a built-in data structure called a table/dictionary/associative-array. If you want to implement some sort of switching behavior you can do a switch on the `tag`, or encode the tag in the type system, and use dynamic dispatch.

Some programming languages have support for asynchronous calls. That programming language has a built-in scheduler of sorts. You can use it, or build your own, (or use the OS!).

A state machine, I think, is a great example of the same idea. Your CPU has a bunch of state (e.g. the program counter), and your programming languages has a bunch more state (like the current stack frame, the line number). You can encode your state machine in that, or you can model it explicitly. How well you can do it "implicitly" depends on other language features, like whether you have coroutines.

I think it's challenging, without expertise that might come only from having solved an identical problem already, to know ahead of time when to use these built-in things or roll your own. When you mention testing, I think that's a great example of expertise you've acquired. If you would like to test certain invariants in your state machine, e.g. "a transition from A to B never happens", then you're going to have a hard time doing so if your state machine's state is encoded in the line number of your language interpreter or the program counter, or whatever.

tartoran3• 6 years ago

They can be useful though, like once in a blue moon on a white boarding session with non-technical users, explaining a bug or something like that

DonHopkins6• 6 years ago

They're great for compressing lyrics!

Rick Flow:

https://pbs.twimg.com/media/DHnyCwiXsAAFyzq.jpg

Circumstances In Which Whipping It May Be Appropriate:

https://gypsywitchcampfire.files.wordpress.com/2015/08/whip-...

Total Eclipse of the Heart:

https://i.pinimg.com/originals/86/17/e8/8617e878f9c33ab3a3ba...

We Will Rock You:

https://www.edrawsoft.com/template/lyric-flowchart.png

Let It Be:

https://i.pinimg.com/originals/a7/74/b5/a774b576f45a6eb71a42...

All You Need Is Love:

https://www.researchgate.net/profile/Alex_Ruthmann/publicati...

Modern Love:

https://i.pinimg.com/originals/8f/fc/9a/8ffc9a199caa1da49ec1...

anigbrowl2• 6 years ago

You can use them for just about anything once you get used to the idea of dynamic nesting. I'm particularly fond of this implementation:

http://www.dsprobotics.com/applications.html

chrisseaton• 6 years ago

These graphs are how the compiler I work on represents your programs while it's compiling them!

throwaway17_173• 6 years ago

This is essentially the point I made in a comment above, these representations are valid considerations for a programmer to weigh when selecting abstractions and constructs to implement some functionality. But it seems like very few people agree.

notacoward4• 6 years ago

Pretty neat. Three things that occurred to me while reading it.

(1) Makes it pretty clear why exceptions are even more of a control-flow nightmare than goto. What a messy graph.

(2) The 'defer' diagram is a big WTF. Couldn't even figure out which box is supposed to represent which statement in the example.

(3) I'd love to see a graph of the control flow when you throw in a few spurious lambdas like "advanced" C++ programmers tend to do (and similar in a few other languages). Might even make exceptions look good.

dabei• 6 years ago

Exception is a nightmare only if you use it as a general purpose control flow mechanism.

notacoward4• 6 years ago

Unfortunately, many do. When that includes popular libraries and frameworks, "abuse" becomes idiomatic or even strictly necessary. When it's in the language itself, such as Python's use of KeyError or StopIteration, that's even more true. Since better alternatives exist for most exception use cases, I'm of the opinion that direct language support was a bad idea. A more general and explicit cousin of signal handlers would suffice for those few "stop the world" cases, and can be done via library functions. Optional types, multiple return values, or plain old error codes (I like Zig's "non-ignorable error code" approach) suffice for the rest.

DonHopkins6• 6 years ago

That's the exception that proves the rule.

lwb3• 6 years ago

My impression was that the article made the exceptions graph much more complicated than it needed to be. Each function doesn’t need three boxes, and they don’t need to each throw exceptions twice. IMO exceptions are much cleaner in practice and are great for things like “kill this script” or “throw a 500 error”.

edflsafoiewq3• 6 years ago

Actually the exceptions graph is simplified. The code to perform unwinding is not depicted.

ken• 6 years ago

If you think exceptions look messy as a flow chart, try conditions! It’s be like exceptions x come-from.

And yet in practice, it’s really not that confusing. Expressivity counts for more than the number of branch opcodes generated by the compiler.

DonHopkins6• 6 years ago

It all boils down to "flaggy code" -vs- "spaghetti code" (or vexillology -vs- pastafarianism).

https://wiki.c2.com/?GoTo

avodonosov• 6 years ago

exceptions are simple and convenient

DonHopkins6• 6 years ago

Except when they're not.

bibyte• 6 years ago

My takeaway was the exact opposite of yours. For example the goto graph seems very intuitive and simple. But it is much more complex to reason about compared to exceptions. My takeaway was that simple graphs like these can't really explain the pros and cons of high level programming constructs.

perthmad• 6 years ago

It's even clearer when you consider higher-order functions. These diagrams are only able to represent functions of order at most 2, i.e. what is called "dependency injection".

beetwenty• 6 years ago

The tradeoff in goto-vs-exception is that a goto needs an explicit label, while an exception allows the destination to be unnamed, constrained only by the callstack at the site where it's raised.

That makes exceptions fall more towards the "easy-to-write, hard-to-read" side of things; implied side-effects make your code slim in the present, treacherous as combinatorial elements increase. With error codes you pay a linear cost for every error, which implicitly discourages letting things get out of hand, but adds a hard restriction on flow. With goto, because so little is assumed, there are costs both ways: boilerplate to specify the destination, and unconstrained possibilities for flow.

Jumping backwards is the primary sin associated with goto, since it immediately makes the code's past and future behaviors interdependent. There are definitely cases where exceptions feel necessary, but I believe most uses could be replaced with a "only jump forward" restricted goto.

jfkebwjsbx• 6 years ago

when you throw in a few spurious lambdas

What do you mean?

zozbot2343• 6 years ago

There's actually a fairly natural way of representing Result-like types (including exceptions) in a flow chart. Draw multiple "exit" terminals for the function, one for "success" and one for each error case. Then a function invocation can have multiple flowlines leading from it, one for each case. And one can "rethrow" the exception quite naturally, by having a flowline for a "rethrown" exception lead to an exit terminal of its own. This also applies by analogy to the case of multiple entry terminals, which come up most naturally when desugaring async functions.

(It's actually even simpler than that when accounting for the functor and monad properties of Result<T, Err>, but the graphical representation for a "functor" or "monad" is a bit more complex; these would be drawn as labeled regions, and functor and monad properties would describe how such regions can be "merged" or "combined".)

rovolo• 6 years ago

RE (2): Defer. The diagram has an extra box in the control flow which is unnecessary. You can label the big boxes from top to bottom like so: A E B <unnecessary> D C.

A good use case for understanding the control flow of 'defer' is when cleaning up resources.

    mutex.lock();
    defer { mutex.unlock(); }

    val f = File.open(filename);
    defer { f.close(); }

    // write to file

It's a nice construct because it keeps construction and destruction close together instead of far apart

    mutex.lock();
    val f = File.open(filename);

    // write to file

    f.close();
    mutex.unlock();

LessDmesg• 6 years ago

(1) There's nothing messy about that graph. It's just two nested function calls. An exception by itself is just a goto to the catch block.

poiuyt098• 6 years ago

yep, the goto example is doing something completely different and less than the exception code, of course it will look more messy.

tel• 6 years ago

This sort of formalism is bad for handling multiple returns and thus exceptions. For instance, they become very simple in continuation passing style whereas GOTO is difficult.

Flowcharts feel like a simple and universal way of talking about, well, control flow, but they imply a certain kind of bias toward a kind of reasoning which isn't necessarily all that better than code itself.

antpls2• 6 years ago

(2) The 'defer' diagram is a big WTF. Couldn't even figure out which box is supposed to represent which statement in the example.

I found the defer diagram very accurate and understandable, but I already knew what "defer" does.

From the preceding examples, I understand that the little box is an instruction the developer didn't write, but was added automatically. From the graph, I understand that the instructions are executed in a different order from what it's written by the developer (and exactly in reverse order).

tabtab3• 6 years ago

The C-style switch/case construct is obsolete and awkward, and cleaner alternatives exist, such as VB.net's technique. There is no need for "Break".

The following could be added to C-style languages without overlapping with the existing syntax:

     select(a) {
        when 1,2,3 {...}
        when 4 {...}
        when 5,6 {...}
        ...
        otherwise {...}
     }

C# recently added a pattern-matching alternative, but it's still a bit verbose for most needs.

nneonneo• 6 years ago

GCC has had case ranges as an extension for a long time now: https://gcc.gnu.org/onlinedocs/gcc/Case-Ranges.html

It’s a far cry from general pattern matching (a la Rust, Scheme) but it’s helpful in some circumstances. Otherwise, you can also stick multiple case labels together, i.e.

    switch(x) {
        case 1 ... 4:
        case 7:
        case 9 ... 16:
            ...
        default:
            ...
    }

I don’t see why you need to call the C-style construct obsolete and awkward, though. It works plenty well for enumerations, which is basically what it was designed for. If you need to do something more fancy, if/else if chains always work.

tabtab3• 6 years ago

Ranges are nice, but not a replacement for sets. (Allow both!) The main "fix" I propose is to get rid of the Break statement and the very need for it. If you have set-based lists, you don't need "fall through" behavior because you can have more than one item per matching expression.

The Break statement is error prone because it's easy to forgot. Some languages "solved" that by making Break required; but if it's required, then it's superfluous: code-bloating eye clutter. If you never used a language that didn't need "Break" you may not understand how annoying it is to go back.

My suggestion above allows C-ish languages to add a modernized version and yet keep the existing construct for backward compatibility. In other words, the old one would be "deprecated".

lwb3• 6 years ago

The point this article makes most clear is exactly to what extent C++ has the attitude of “screw it, let’s put it in”. There are only a handful of constructs listed that C++ doesn’t implement.

Also, TIL about “long jump”. Seems like a feature I’d never use in a million years, but maybe it has its applications.

TFortunato• 6 years ago

LongJmp can be used as a way to implement exceptions at a low level, especially in languages like C, where you dont have them as a language construct.

You call SetJmp, where you would want to put your try/catch blocks, then no matter how deep down some call stack you go, if an errir occurs, you can immediately jump back to where you called setjmp and handle it / report the error or whatever, rather than having to handle and bubble up the error by at every intermediate level, "returning" your way up the call stack.

inetknght4• 6 years ago

As someone who's self-taught everything, this is... awesome. It's exactly what I needed to be able to up my game in describing code to management using the flowcharts they've asked for.

zabzonk2• 6 years ago

In case you haven't gleaned it from the majority of comments here, flowcharts are a terrible way to describe code, particularly modern, multi-threaded code that uses exceptions. Don't go there.

crimsonalucard• 6 years ago

This is because flow charts are two dimensional. What you need is a 3rd dimension to represent parallelism. These programs are better represented as 3d structures rather then 2d flow charts or even text.

inetknght4• 6 years ago

I quite agree. Unfortunately management wants single-threaded code and wants it documented with flowcharts. So right now there's lots (!) of clouds detailing "this calls into another API documented in another flowchart..."

anigbrowl2• 6 years ago

Obviously you don't like them, but flow based programming is pretty great actually.

throwaway17_173• 6 years ago

If you find these flowcharts instructive, and I think that you are well founded in doing so, good on you. A majority of other comments seem to be of the opinion that pointing out the complexity of control flow generated by the constructs in a language is a negative. It certainly seems like the prevailing attitude is ‘if I can’t see it, it doesn’t exist.’ But you said you were working on game code, so I will encourage you to keep thinking about the complexity of the choices you make in which constructs to use and don’t buy into the thought that says performance implications are not a really concern.

inetknght4• 6 years ago

you said you were working on game code

Actually, I didn't. I said I wanted to "up my game" which is a phrase commonly meaning "to get better". Said another way: I needed to get better at describing code to management.

I will encourage you to keep thinking about the complexity of the choices you make in which constructs to use

Indeed, management generally wants simpler code even at the cost of performance. Simpler code generally translates to cheaper developers and cheaper maintenance.

don’t buy into the thought that says performance implications are not a really concern

I actually write DNA analysis software. Performance implications definitely are a concern. :)

But performance is useless if I'm the only developer who understands how it all comes together (eg, high bus factor). So I've been writing a lot of documentation to that end, from file-level down to the systems-level and bit-level descriptions. I really would like better support for diagrams in markdown.

theaeolist• 6 years ago

Have a look at these diagrams for PL concepts, but done formally and with execution rules:

https://tnttodda.github.io/Spartan-Visualiser/

azhenley• 6 years ago

Best article I have read in a while. I'm going to try to incorporate this into my PL course.

MadWombat• 6 years ago

I don't know about everyone else, but to me these are confusing as fuck. In continue/break/early return diagrams, there is no second condition, so it is not clear when/why the dotted line logic path happens. The "no fall-through" has so many arrows it takes some zen meditation to figure out what it means. And the exception diagram is just amazing, does the catch block get executed no matter whether there was an exception or not? Because there is an arrow leading to it from the regular, no exception, path. I could go on, but it becomes progressively more and more bizarre.

grawprog• 6 years ago

I don't know about everyone else, but to me these are confusing as fuck.

I was alright right up until it got to exceptions. Simple statements are fairly nicely represented in flowchart form and almost condense the information a bit. Then it hits exceptions and everything after that just got so convoluted it became pretty ridiculous. Imagine trying to write out even 100 lines of modern code like that. You'd need a page the size of the side of a barn just for that.

keithb-• 6 years ago

I agree. The semantics even within this set of flowcharts is confusing: blocks start out representing statements but by the time you get to Dependency Injection, they represent anything (library, service, etc.). Also the dotted-line vs solid line doesn't help. With Goto or Exception, the dotted line is the process, not the alternative which is solid. Those need to be inverted because "normal" flow of control from statement to statement is altered and the "exceptional" flow is now active and other statements are ignored. Just waiting for someone to say "we tried this with UML already. please just stop."

martinfjohansen2• 6 years ago

Hi, I am the author of the article, thanks for noting an error in the exception and finally diagrams! I have fixed the error where controlflow always went to the catch block.

raslah• 6 years ago

I actually really like flowcharts, though they are somewhat inefficient to draw out more complex structures, they are great for working out small sections of thorny logic. The only issue I sort of take those in the article is the physical flow is a little distracting when decisions don't branch laterally. having them continue top to bottom sort of throws me off. perhaps its just because i draw them with branches to the side.

Supermancho• 6 years ago

This is a wonderful idea, but by the given numbering scheme, I can identify a slew of problems.

[1a. If] Note This is the first time we see synchronous calls, decisioning, and the representation makes no specific callout to the structure. The structure IS the case.

[4. Break] InconsistencyConfusion This is the first time we see a specific part of the flow called out as the structure (it isn't a structure). This is flow control, not a construct. This confusion plagues the rest of the document.

[7. Switch (No Fall-Through)] InconsistencyConfusion This is the same as If/elseif.../else/, but the post goes with the oddly specific "switch". Would be more appropriate as [1c. if/elseif.../else] and a [1d. Switch] - The different terminology if/switch does not change the fact they are the same structure. Grouping Switch-type by name is a bad choice.

[9. Local Goto] Omission The Goto example has no exit node.

[11. Exceptions] Mistake The exception travels the stack, meaning (from the perspective of the original parent function), from grandchild to the child, to the parent catch.

[12. Finally] OmissionConfusion Finally should be it's own block, since it is treated as such and has an implicit catch mechanism, even if it's not always required in the syntax.

[13. Blocking, Synchronous Calls] Confusion This is rather pointless. All the flows, prior, were blocking. Now introducing another metaphor that changes past examples is inconsistent. Blocks which are synchronous (blocking) are represented by 2 different forms. It's unnecessary.

[14a. Non-Blocking, Asynchronous Call, Callback] InconsistencyConfusion There is a whole function called, which should be represented by a starting and ending node.

[14b. Device Input] InconsistencyConfusion This isn't even a different construct. Event handling is what this is and is poorly represented, in the same way as 14a.

[15. Framework] MistakeConfusion This isn't a construct, nor is it an accurate representation. Frameworks are a collection of idioms, which usually has little to do with constructs (as defined in the beginning). It feels like the author has gone off the rails here.

[18 Come-from & 19 Aspects & 21 Destructor] Confusion? The size of the block is supposed to indicate a specific syntax, which is inappropriate for describing logical constructs. They should be full sized and optionally labeled blocks, as they are evaluated.

[20 Dependency Injection] Confusion This is another "timing adds a new way to represent things" issue. There's no difference between an Aspect and DI, logically.

[22. Defer] *Confusion Adding data (even a function) to a separate stack, which is called later, does not make the diagram presented.

All in all, this needs work. Even the grouping description at the bottom does nothing to help make this more useful.

DonHopkins6• 6 years ago

The Nassi-Shneiderman diagram is one way of representing structured program flow by dividing up a two-dimensional area. It can't represent unstructured gotos and exceptions, though.

https://en.wikipedia.org/wiki/Nassi%E2%80%93Shneiderman_diag...

A Nassi–Shneiderman diagram (NSD) in computer programming is a graphical design representation for structured programming. This type of diagram was developed in 1972 by Isaac Nassi and Ben Shneiderman who were both graduate students at Stony Brook University. These diagrams are also called structograms, as they show a program's structures.
Overview: Following a top-down design, the problem at hand is reduced into smaller and smaller subproblems, until only simple statements and control flow constructs remain. Nassi–Shneiderman diagrams reflect this top-down decomposition in a straightforward way, using nested boxes to represent subproblems. Consistent with the philosophy of structured programming, Nassi–Shneiderman diagrams have no representation for a GOTO statement.
Nassi–Shneiderman diagrams are only rarely used for formal programming. Their abstraction level is close to structured program code and modifications require the whole diagram to be redrawn, but graphic editors removed that limitation. They clarify algorithms and high-level designs, which make them useful in teaching. They were included in Microsoft Visio and dozens of other software tools, such as the German EasyCode.
In Germany, Nassi–Shneiderman diagrams were standardised in 1985 as DIN 66261. They are still used in German introductions to programming, for example Böttcher and Kneißl's introduction to C, Baeumle-Courth and Schmidt's introduction to C and Kirch's introduction to C#.
Nassi–Shneiderman diagrams can also be used in technical writing.

When Ben Shneiderman and Ike Nassi (who were grad students at the time) submitted their paper about them to Communications of the ACM, it was quickly rejected on October 4, 1972, with the most brutal rejection letter Ben Shneiderman has ever received.

But then they submitted it to the unrefereed ACM SIGPLAN, where it was published in August 1973, and since then it has been cited many times, widely implemented by many tools, and used for educational and documentation purposes. It's a great example of the importance of persistence for people whose new ideas are brutally rejected by respected authorities:

Flowchart techniques for structured programming:

https://dl.acm.org/doi/10.1145/953349.953350

Scan of the brutal referee's report:

https://www.cs.umd.edu/hcil/members/bshneiderman/nsd/rejecti...

My first thought was to write a referees report which would by its sarcastic nature be funny. For example, I thought of writing that it was a sound, useful theory, but it wasn't practical because it would be difficult to design flowcharting templates to be manufactured and sold.
I guess, however, that it is best to come right out and say that I feel the best thing the authors could do is collect all copies of this technical report and burn them, before anybody reads them. My opinion is that it shows the inexperience and ignorance of the authors with respect to programming in general, and their misunderstanding of so-called structured programming.
To say that [BEGIN body END] should be written as [NS diagram] is ridiculous. Even more ridiculous is having to write [DO i=1 TO N; DO J=1 TO N; S = 0; DO K=1 TO N; S=S+A(I,K)*B(K,J) END C(I,J)=S END END] as [NS diagram].
The authors mention that "the ease with which a structured flow-chart can be translated into a structured program is pleasantly surprising". My retort is "yes, just erase those silly boxes!"
Flowcharts are a crutch we have invented to try to understand programs written in a confusing style. This was due to our ignorance of the programming process and what was needed -- after all, programming is only 20-30 years old. So-called "structured programming" helps to limit us to, as Dijkstra calls them, "intellectually manageable" programs, in which case flowcharts are completely useless and in fact a hindrance to programming. They shouldn't be used.
I shudder at the thought of further explorations revolving around the context-free nature of this [flowchart] language.

Ben's rejection letter story:

https://www.cs.umd.edu/hcil/members/bshneiderman/nsd/rejecti...

Rejection letter from the Communications of the ACM
Ben Shneiderman, June 12, 2003
Our submission of the structured flowcharts to the Communications of the ACM was quickly rejected, on October 4, 1972, by the Programming Languages Editor David Gries of Cornell University. He included a single anonymous reference letter which is on paper that has a Cornell University watermark. I assume Gries gave our paper to one of his colleagues (you can play the guessing game too), who wrote the most brutal rejection letter I have ever gotten.
The reviewer wrote: "I feel that the best thing the authors could do is collect all copies of this technical report and burn them, before anybody reads them." As graduate students, this stinging rejection shocked us, but we kept getting enthusiastic responses from people around us. We sent the paper to the unrefereed ACM SIGPLAN Notices, where it was published in August 1973. It didn't take long for others to produce extensions, software tools, and applications of structured flowcharts.
The next problem was theft of the idea. I had sent a draft to respected colleagues, and soon others published slight variations. One of these respected colleagues was Ned Chapin, who greatly troubled us by publishing what he called 'Chapin Charts.' A friend of mine sent me his published paper with a note encouraging me to sue. For several years I feared that Chapin's reputation and his frequent professional seminars would wind up leaving the idea tied to his name, but as the decades passed, the ending has proved to be a happy one. We called the idea 'structured flowcharts, but they are widely known as Nassi-Shneiderman Diagrams.
Another problem was the appearances of patents for variations on our idea, but these have not limited the widespread recognition we have gotten over the years.
I wish every graduate student or young inventor would have the pleasure of seeing his/her ideas spread so far and influence the work of so many people. I also hope that the story of the bold rejection of our novel idea and its eventual international success, is an inspiration for anyone whose new ideas are rejected by some respected authorities.

More on Ben Shneiderman and NS diagrams:

https://news.ycombinator.com/item?id=11368430

https://news.ycombinator.com/item?id=11370099

https://news.ycombinator.com/item?id=22093072

proc0• 6 years ago

I love this! Visually seeing computation flow is great for understanding what the code is doing.

_0ffh• 6 years ago

Pretty decent, but covers the pre-test loop as "loop" (unqualified), omitting the post-test loop.

edflsafoiewq3• 6 years ago

The goto diagram contains an erroneous arrow and an extra block. It should look like

       o
       |
       v
    +--□
    |
    |  □<-+
    |  |  |
    |  v  |
    +->□--+

PacifyFish• 6 years ago

What did the author use to make the charts?

martinfjohansen2• 6 years ago

I used "yEd live".

edflsafoiewq3• 6 years ago

Speaking of reasoning, I believe a Hoare proof of correctness for a flowchart is

* a choice of a precondition and postcondition, Pre(B) and Post(B), for every basic block B

* for every basic block B, a proof that {Pre(B)} B {Post(B)}

* for every arrow a : B1 -> B2, a proof that Post(B1) /\ Cond => Pre(B2) where Cond is the condition for the arrow to be taken

emmanueloga_• 6 years ago

I think flow charts are a lot more useful when the granularity is more coarse: the boxes should represent functions, not the logic inside.

    compute thing -> predicate true ------> compute some other thing
        |         -> predicate false ->|
        \---------------loop-----------/

... etc ...

0xff00ffee2• 6 years ago

Raise your hand if you at first thoroughly expected to mock this, and then giggled at "function" (vs. subroutine), patted yourself on the back for knowing everything up until ... ASPECT? DAFUQ IS ASPECT?

Just me? Ok, I'll show myself out.

Great way to visualize. I think Exceptions, Finally (and Promises) got a little messy, but would make a good poster.

quelltext• 6 years ago

I'm sure you're not the only one, but yes AOP is something a lot of people interested in programming languages have likely heard of at some point.

antpls2• 6 years ago

The actual question is : did it allow you to quickly understand the "aspect" concept by using a common graphical representation? If yes, that's a win

0xff00ffee2• 6 years ago

No. The explanation isn't clear: why is g() inserted at one point and h() inserted at another. This needs to be explained.

However, from what I observe, "aspects" look a lot like Common LISP Object System (CLOS) before/after/around methods.

dependenttypes• 6 years ago

The break one does not make a lot of sense to me. Shouldn't they use another rhombus and a solid line instead? Same for continue and early return. Similar thing holds for goto.

richdougherty• 6 years ago

Pretty neat, but notably missing some of the more functional control flow concepts: tail calls, call with current continuation, delimited continuation, etc.

Flowcharts of programming language constructs

Related Stories