Gilding

The module system outlined above should work well for SLIB. Using load-module, most SLIB modules will work without modification.

Correspondents have expressed concern over a variety of issues.

• Making modules a disjoint datatype involves only writing the usual boilerplate about module?.
• define-internal is not strictly necessary and can be emulated with convoluted coding. But it is convenient and directly satisfies one of the capabilities people expect from a module system. define-syntax-internal is not necessary because letrec-syntax will suffice.

  syntax: define-internal

  A define-internal behaves identically to top level define except that an identifier defined with define-internal will not be exported.

• Per Bothner has pointed out that this proposal is quite different from other module proposals. He suggests it would be less wrenching for users if a declarative export syntax were supported.

  syntax: export ident1 ident2 ...

  ident1, ident2, ... should be identifiers. If an export form occurs at top level in code for a module (argument to module, make-module, or load-module), then the returned binding contour is modified as follows: Only ident1, ident2, ... are exported. It is an error if a module has more than one export statement. It is an error if an identifier occurs more than once in an export statement. It is an error if ident1, ident2, ... are not all defined at top level in the code for the module containing the export statement.

  So far, export has been winning the popularity contest with define-internal.
• At least one Scheme compiler gives only negligible speed improvement over interpretation when integrable declarations are lacking. I believe all Scheme compilers could compile the type of modules discussed above with good benefit because of the INTEGRABLE guarantees. Given that compilers could produce reasonable code without platform specific declarations, and given that the extent of the source (which code gets compiled) is well delineated by the module boundary, it seems reasonable to also propose a uniform compiler interface.

  procedure: compile-module-file filename

  compile-module-file compiles the module specified by its string filename argument and returns a value suitable for passing as an argument to import-compiled-module, or #f if the compilation was not successful. If the value returned by compile-module-file is a string, then it can name a file produced by compile-module-file, which can be passed to import-compiled-module in the future without re-compilation.

  procedure: import-compiled-module compiled-module

  Behaves as import-module does, but for a compiled module.

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