3.3 Module initialization

Initializing a module means evaluating, at runtime, its top level forms (global bindings are top level forms).

When a module, module1, imports a module, module2, module2 is initialized before module1. Modules are initialized only once, nothing being done if a module already met during initialization is met again. Library modules are initialized before user modules and imported modules are initialized in the same order as they appear in import clauses.

Here is a first example with two modules. First the module foo:

;; module foo
(module foo
   (main main)
   (import (bar "bar.scm")))

(define (main argv)
   (print "argv: " argv))
(print "foo")

Then the module bar

;; module bar
(module bar)

(print "bar")

These can be compiled into the executable a.out with:

$ bigloo -c foo.scm
$ bigloo -c bar.scm
$ bigloo foo.o bar.o

Execution of a.out produces:

$ a.out
   -| bar
      foo
      argv: (a.out)

The explanation is:

• module foo contains the program entry point so this is where initialization begins.
• because foo imports module bar, bar must be initialized before foo. This explains why the word bar is printed before anything else.
• module initialization for foo is completed before main is called. This explains why word foo is printed before main is entered.

Let’s consider another example with 3 modules:

;; module1
(module module1
   (main main)
   (import (module2 "module2.scm")))

(define (main argv)
   (print "argv: " argv))

(print "module1")

The second module:

;; module2
(module module2
   (import (module3 "module3.scm")))

(print "module2")

The third module:

;; module3
(module module3
   (import (module1 "module1.scm")))
 
(print "module3")

Compile with:

$ bigloo module1.scm -c
$ bigloo module2.scm -c
$ bigloo module3.scm -c
$ bigloo module1.o module2.o module3.o

Execution produces:

$ a.out
   -| module3
      module2
      module1
      argv: (a.out)

The order of module initialization can be explicitly specified using with and use clauses.

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