From: "andrew cooke" <andrew@...>
Date: Sun, 12 Aug 2007 20:04:09 -0400 (CLT)
This largely states the obvious, but boy, did I need this earlier today. So perhaps this will help someone else. OK, so the context is - you want to use a Scheme. You also want to be able to use and share libraries. And you want unit tests. And you'd rather not write code specific to one particular Scheme. But you want namespaces/packages... So the solution, as far as I can see, is to use Snow (aka Scheme Now) - http://snow.iro.umontreal.ca/ - plus whatever Scheme takes your fancy (I am using Gambit because the idea of Erlang with a better syntax seems pretty cool - if that makes no sense, check http://lambda-the-ultimate.org/node/841). But how does all this work? That is the obvious thing that wasn't... First, you install whatever Scheme you want (if you're running Linux you may already have Guile installed). I installed Gambit. It's the usual configure and make; pretty painless. Next, you install Snow. That means downloading the "generic Snow" and then doing the config and make install process. One you've done that (and set your paths), you end up with a couple of utilities. First, snowman, which is like yast or apt, or rpm or cspan, whatever - a package manager that lets you install packages. It's documented 2/3 of the way down this page: http://snow.iro.umontreal.ca/?tab=Documentation Second, you have a program called "snow" which is what you use to invoke your scheme code. I wasn't expecting this, but it makes sense - it hides away whatever magic is needed to convert your particular Scheme to support the cross-platform snow API. The simplest way to use snow is as an interpreter (you can also compile code using "snow --compile" but I've not explored that yet). The Snow docs give the following example. Note that the first line is some kind of bash magic that invokes the same file using "snow" (I think it is written like that so that the syntax is acceptable to bath bash and scheme). ":";exec snow -- "$0" "$@" (package* go/v1.0.0 (require: hostos/v1) (require: fixnum/v1)) (define (double x) (snow-fxarithmetic-shift-left x 1)) (test* (expect* (= 8 (double 4)))) (write (double (string->number (cadr (snow-command-line))))) (newline) To see that working, put it in a file called "go.scm", then chmod +x so that it's executable, and invoke it with an argument: > ./go.scm 500 1000 That's it, really. That is running (in my case) Gambit, with all the relevant Snow bits added. So you get the module/namespace functionality (the package* bit) and the unit test functionality (test*, expect*). One final cute trick. I said earlier that Guile is probably already installed on Linux. That's true in my case, and Snow can invoke scripts on "all schemes", which makes testing compatibility easy. Here's how: > SNOW_HOST=all ./go.scm 500 ------------------------------------------------------------ gambit 1000 ------------------------------------------------------------ guile 1000 Once you grok the above, the Snow site documentation makes a lot more sense. All this is there anyway (what got me started was someone sending me a cut+paste of the relevant sections!). But somehow, for me at least, the "big picture" took time to form. Andrew