Parameterized Modules

[zaphar]

UCG already has a lot of tools for reuse in the form of macros and copy expressions. However macros don't compose very well and Copy Expressions only work at the level of a single tuple. If you need several tuples and macros to work together and don't want to require the user to compose them manually then some way to have a Parameterized Module system is required.

[zaphar]

Proposed Syntax for a ucg module:

let my_mod = module {
   // arguments are specified as a tuple with default values specified for each argument.
    hostname="",
    port=0,
    db="localhost",
    db_user="admin",
    db_pass="password"
} { // mods do not close over their environment.

    // this binding is not visible outside of the module. should be at the time of definition?
    // or path should be rewritten to be absolue before instantiation.
    import "../../shared.ucg" as shared;

    // processing should be delayed till module instantiation.
    let base_config = shared.mk_site_config(mod.hostname, mod.port); 

    let config = base_config{ // processing should also be delayed.
        dbs = self.dbs + [
            // mod is a special selector inside of a module that refers to the parameters
           // of the module.
            shared.mk_db(mod.db, mod.db_user, mod.db_pass)
        ],
    };
};