Think of it as separation of runtime and compile phase. A module may have imports and exports that are only visible at compile time; this is exactly what for-syntax import/export does.

for-template is a little harder to explain, you can think of it as injecting dependencies in modules who are using your module. It is useful if you have a module that is designed to be imported for-syntax (eg macro utilities or procedural macro implementations). If you generate code that refers to symbols not in your scope but which must be available at runtime (well, at phi-1 relative to the current phase) in the module that is importing you, then you import the relevant modules for-template and the expander does the rest.

-- vyzo

On Tue, Oct 22, 2019 at 5:57 PM Adam adam.mlmb@gmail.com wrote:

Ah great, thanks - it's almost fully clear now.

|for-syntax| and |for-template|, is their motivation that |phi:| takes a set of *identifiers* - e.g. (export … (phi: +1 make-protocol-info protocol-info? …)) and hence a separate form is needed to import/export whole modules on given phi:s and that's what these are for e.g. (export … (for-syntax bigmodulename))?

On Tue, 22 Oct 2019 at 22:24, Dimitris Vyzovitis vyzo@hackzen.org wrote:

...

They are documented in the reference: https://cons.io/reference/core-prelude.html#module-sugar

-- vyzo

On Tue, Oct 22, 2019 at 5:12 PM Adam adam.mlmb@gmail.com wrote:

...

Hi Vyzo,

The core prelude ( https://github.com/vyzo/gerbil/blob/master/src/gerbil/prelude/core.ss) defines some extensions to |import| and |export|.

Bumped into studying this in proto.ss, which contains (export ... (struct-out !rpc ...) ...). struct-out can be understood from its use - it's for exporting a structure with its constructors, accessors, mutators. (struct-out's definition code is totally unreadable to me though.)

All of these are undocumented, may you want to comment on what they are for also with a single use example (or add to some documentation section in your guide)?

Thanks! Adam

defsyntax-for-import-export:s:

• for-syntax
• for-template

defsyntax-for-import:s::

• only-in
• except-in
• rename-in
• prefix-in
• group-in

defsyntax-for-export:s:

• except-out
• rename-out
• prefix-out
• struct-out