Hi Julian, Thanks for the feedback.
Regarding C++ exceptions: exceptions are not really nice. They can just make your function return without you even knowing it (forgetting a `try/catch` or not knowing it may be needed, which is C++'s fault and probably could have been done better). Also, they require complicated operations. You can read a small complaint about it here: http://stackoverflow.com/a/1746368/912144 and I'm sure there are many others on the internet. Regarding OCaml option types: in fact I did think of this separation after learning about monads (through Haskell though). However, personally I don't see how monads could be introduced in C without majorly affecting syntax and ABI. Regarding the syntax: You are absolutely right. I don't claim that this particular syntax is ideal. I'm sure the many minds in this mailing list are able to find a more beautiful syntax, if they are interested in the idea. Nevertheless, the following code: x = foo() + bar(); doesn't do any error checking. I.e. it assumes `foo` and `bar` are unfailable. If that is the case, there is no need for a `!! goto fail_label` at all. I personally have never seen such an expression followed by e.g. if (x ....) goto foo_or_bar_failed; On the other hand, something like this is common: while (func(...) == 0) which, if turned to e.g.: while (func(...) !! break) or fail_code=0; while (func(...) !!= fail_code, fail_code == 0) could seem awkward at best. My hope is that through this discussion, we would be able to figure out a way to separate success and failure of functions with minimal change to the language. My syntax is based on having the return value intact while returning the success-failure and error-code in registers both for speed and compatibility and let the compiler generate the repetitive/ugly error-checking code. Other than that, I personally don't have any attachments to the particular way it's embedded in the grammar of GNU C. On Mon, Mar 10, 2014 at 3:50 PM, Julian Brown <jul...@codesourcery.com> wrote: > On Mon, 10 Mar 2014 15:27:06 +0100 > Shahbaz Youssefi <shab...@gmail.com> wrote: > >> Feedback >> ======== >> >> Please let me know what you think. In particular, what would be the >> limitations of such a syntax? Would you be interested in seeing this >> extension to the GNU C language? What alternative symbols do you think >> would better show the intention/simplify parsing/look more beautiful? > > I suggest you think about how this is better than C++ exceptions, and > also consider alternatives like OCaml's option types that can be used > to achieve similar ends. > > For your suggested syntax at function call sites, consider that > functions can be called in more complicated ways than simply as "bar = > foo();" statements, and the part following the "!!" in your examples > appears to be a statement itself: in more complicated expressions, that > interleaving of expressions and statements going to get very ugly very > quickly. E.g.: > > x = foo() + bar(); > > would need to become something like: > > x = (foo() !! goto label1) + (bar () !! goto label2); > > And there are all sorts of issues with that. > > Anyway, I quite like the idea of rationalising error-code returns in C > code, but I don't think this is the right way of going about it. > > HTH, > > Julian
