4 ms·

h2s: Can you explain to us what exactly is the difference between the implementation of flow control during exception throwing and all the other kinds of flow c

by andyjpb 14y ago

h2s: Can you explain to us what exactly is the difference between the implementation of flow control during exception throwing and all the other kinds of flow control (including, but not limited to, stack popping).

eps 14y ago
Do you mind clarifying who is these "us" you are referring to?
gleamer 14y ago
Exceptions, as implemented in languages such as C++, also influence the flow of execution. Therefore, technically, exceptions are a kind of control flow structure. But it doesn't mean that abusing exceptions as control structures is a reasonable idea.
astrobe_ 14y ago
IIRC no standard flow-control construct can do non-local returns (and that's where the Evil lies).
- andyjpb 14y ago
  How about call/cc and setjmp/longjmp ?
  - emn13 14y ago
    And those control flow methods are also widely considered to be tricky and cause a maintenance burden.
    - shurcooL 14y ago
      Just making an observation here. The reason they are tricky and cause a maintenance burden is because they create non-obvious dependencies. You'd have to read a lot of seemingly unrelated code to spot them. Without the explicit knowledge of these dependencies, your changes will have unexpected consequences. (Hence, in a system that tracks all dependencies perfectly, this might not be a problem. This is an experiment I'm trying to run right now.)
      - astrobe_ 14y ago
        Exceptions have been called "glorified goto" for a reason. In fine, the OP says that GOTOs are perfectly acceptable.
      - shurcooL 14y ago
        Interestingly, what I'm considering seems to be very similar to http://en.wikipedia.org/wiki/Dataflow_programming http://en.wikipedia.org/wiki/Dataflow_programming. Yet it doesn't seem like that has spread to be the most common type of programming. Why not? What makes dataflow programming not viable for creating software today?
  - BruceM 14y ago
    Or my comment elsewhere in this thread about condition systems in Common Lisp and Dylan.
    - astrobe_ 14y ago
      I said standard. Since that condition system is proper to Lisp, it is henceforth non-standard. And come on, you don't see setjump/longjump every 10 LOC, not even every 10 source file.
      - BruceM 14y ago
        In Lisp, every bind-exit or unwind-protect may be doing something like a setjmp. That's how it is implemented in the C runtime for Dylan as well. In JavaScript, you have the ability to break to a label to escape nested loops. That's a limited form of a non-local exit. Ola Bini was working with a condition system in his experimental / hobby language Ioke as well. These ideas get around. You'd probably be surprised at how some of this works in Smalltalk as well.

by andyjpb 14y ago

eps 14y ago

Do you mind clarifying who is these "us" you are referring to?

gleamer 14y ago

Exceptions, as implemented in languages such as C++, also influence the flow of execution. Therefore, technically, exceptions are a kind of control flow structure. But it doesn't mean that abusing exceptions as control structures is a reasonable idea.

astrobe_ 14y ago

IIRC no standard flow-control construct can do non-local returns (and that's where the Evil lies).

andyjpb 14y ago
How about call/cc and setjmp/longjmp ?
- emn13 14y ago
  And those control flow methods are also widely considered to be tricky and cause a maintenance burden.
  - shurcooL 14y ago
    Just making an observation here. The reason they are tricky and cause a maintenance burden is because they create non-obvious dependencies. You'd have to read a lot of seemingly unrelated code to spot them. Without the explicit knowledge of these dependencies, your changes will have unexpected consequences. (Hence, in a system that tracks all dependencies perfectly, this might not be a problem. This is an experiment I'm trying to run right now.)
    - astrobe_ 14y ago
      Exceptions have been called "glorified goto" for a reason. In fine, the OP says that GOTOs are perfectly acceptable.
    - shurcooL 14y ago
      Interestingly, what I'm considering seems to be very similar to http://en.wikipedia.org/wiki/Dataflow_programming http://en.wikipedia.org/wiki/Dataflow_programming. Yet it doesn't seem like that has spread to be the most common type of programming. Why not? What makes dataflow programming not viable for creating software today?
- BruceM 14y ago
  Or my comment elsewhere in this thread about condition systems in Common Lisp and Dylan.
  - astrobe_ 14y ago
    I said standard. Since that condition system is proper to Lisp, it is henceforth non-standard. And come on, you don't see setjump/longjump every 10 LOC, not even every 10 source file.
    - BruceM 14y ago
      In Lisp, every bind-exit or unwind-protect may be doing something like a setjmp. That's how it is implemented in the C runtime for Dylan as well. In JavaScript, you have the ability to break to a label to escape nested loops. That's a limited form of a non-local exit. Ola Bini was working with a condition system in his experimental / hobby language Ioke as well. These ideas get around. You'd probably be surprised at how some of this works in Smalltalk as well.