m...@markwitmer.com writes: > I'm running into a problem creating custom languages that compile to > Scheme. I have an example here of a simple compiler that takes any > Scheme expression and generates code for creating a Guile module. If I > compile a file using this language and reference the resulting module > from another one that's just written in normal Scheme, it works the > first time when the normal Scheme file gets autocompiled and then fails > subsequently when the cached compiled Scheme file is loaded, telling me > that any reference I make to a symbol defined in (guile) from my > compiled non-Scheme module is undefined. >
A little more investigating helped me find the root cause of this (as usual). It has to do with the semantics of (begin ...), which I don't quite grok totally, but I do know they're different in the top-level environment and elsewhere. If you call `define-module' inside of a (begin ...) interactively (i.e. at the repl), further expressions inside the begin all evaluate as I expect -- inside the newly defined module, with the bindings for (guile) imported and so forth. However, if you compile the same expression and try to use it non-interactively (i.e. in a script), the expressions inside the begin after define-module are evaluted in an empty module, I think. So the solution for compiling code is to make sure that `define-module' is in its own expression at the top of the file like it would be if you created the file yourself. This leads to another question: do expressions in a high-level language need to have a 1:1 correspondence with Scheme expressions? The #:compile function of a language takes one expression in the higher-level language and returns a single expression in the lower-level language, so it looks that way to me. My use case is for guile-xcb, where the root xml tag is read in as a single expression, and it's supposed to generate Scheme code that includes a call to define-module and then a few other expressions to set up context within the module. I can't see a way to do that without wrapping the whole set of expressions in `begin', but that's what creates the problem I described above. I can hack a solution for now but if anyone knows a clean way to do it, that'd be much appreciated. Thanks, -- Mark Witmer
