On 13 October 2011 20:07, Ian Price <ianpric...@googlemail.com> wrote: > Linas Vepstas <linasveps...@gmail.com> writes: > >> I have no clue why it never occurred to me to use the above paradigm, >> I will definitely start experimenting with it. >> >> Any clue on how to indicate that func returns type 'X' ? >> >> I don't know if you were trying to make this point but: if one were to >> code in the above paradigm, and also throw some srfi-9000 syntactic >> sugar at it, one might be able to get something that resembled >> ocaml/haskell type declarations. And, for the code that I deal with, >> this might be the bees knees. > > Just because scheme doesn't have type declarations doesn't mean you > can't add them. I often write code that looks like > > ; partition : (A -> Boolean) Listof(A) -> Listof(A) Listof(A) > (define (partition pred list) ...) > > and I also make heavy use of 'assert', and less frequently, a macro of > mine called 'assert-lambda' which looks like > > (lambda ((a procedure?) (b list?)) ...) > > I don't, in general, check return types, but I do try and make sure that > they obey the declaration comment. Having a built-in type/contract > syntax, like Racket has, would be nice as I could move these comments > into code, but this is better than nothing.
Well, I see two choices: 1) Let the conversation slide, and incorporate above thoughts as 'best practices' into my code. 2) Flame-war. In the spirit of 2), Andy Wingo wrote: > I can't find the source right now, but I think it was Matthias Felleisen > who gave a variant of Greenspun's tenth law, that "any sufficiently > complex Lisp program has a buggy, incomplete ML program in the > comments". So the proposal is: (shout me down, when ready): create a new srfi, defining an ML-like conception of types, so that scheme functions can be annotated with types. The goal here is not so much to do type-checking at run-time, but to allow static type checking. That is, one could create a "type checker tool", which one could invoke ad-hoc, during development, to make sure that my scheme programs are consistent with their handling of types. This is static type checking -- as, for the most part, I am not interested in type-checking during runtime, for two reasons: performance, and also because I want to avoid the hard-to-debug problem where I only pass the wrong type only once in a million. Basically, as a debugging/development tool, everything I've read about ML (e.g. the Jane's street commentary) is that the static type-checking in ML is a powerful means of avoiding developer errors. It'd be neat if I could get this feature in scheme. BTW, as a token nod to C: please be aware that the Linux Kernel folks have been busy creating and extending a static type-checking system for C, which is used extensively in the linux kernel sources. The goal there is to avoid accidentally passing user-space pointers into the kernel (where they are invalid), and to avoid calls to __init routines during runtime (because they no longer exist after initialization). Note that this kind of type-checking is not possible in "ordinary" C. I can't comment on how "well-designed" the system is, but it has been very effective in finding zillions of bugs in the linux kernel. --linas
