using `use`

Large or involved projects may involve Maple modules which rely upon each other. Routines in one module may call routines in another module. Interdependence of modules can have a direct bearing on the available means of successfully utilizing the `use` functionality. In certain situations, some of the ways to utilize the `use` statement can be problematic.

Some such situations, and workarounds, are illustrated below.

The basic description of the `use` statement functionality is,

     The use statement allows you to specify local bindings
     of names, module ``imports'', and operator overriding.

See the help-page ?use for more details.

The implicit short-form version of `use` can cause difficulties. As the projects get larger these difficulties can become a burden. So, one may elect to avoid some forms of `use` in deference to other forms.

Here are some examples to illustrate the difficulties and some of their resolutions.

# Failed definition of module, due to dependency.
>
> m1 := module()
> export f1;
>   f1 := proc(x)
>     use m2 in
>       f2(x);
>     end use;
>   end proc;
> end module:
Error, `m2` is not a module or member
>
>
> restart:
>
# The explicit routine-by-routine long-form of `use` works.
>
> m1 := module()
> export f1;
>   f1 := proc(x)
>     use f2=:-m2:-f2 in
>       f2(x);
>     end use;
>   end proc;
> end module:
>
> m2 := module()
> export f2;
>   f2 := proc(x)
>       sin(x);
>   end proc;
> end module:
>
> m1:-f1(17);
                                    sin(17)
 
>
>
> restart:
>
# Reordering the procedure defns also works, for this example.
# But this may not always be possible, for very involved projects.
>
> m2 := module()
> export f2;
>   f2 := proc(x)
>       sin(x);
>   end proc;
> end module:
>
> m1 := module()
> export f1;
>   f1 := proc(x)
>     use m2 in
>       f2(x);
>     end use;
>   end proc;
> end module:
>
> m1:-f1(17);
                                    sin(17)
 
>
>
> restart:
>
# :- also works, with `use` omitted altogether, with either order.
>
> m1 := module()
> export f1;
>   f1 := proc(x)
>       m2:-f2(x);
>   end proc;
> end module:
>
> m2 := module()
> export f2;
>   f2 := proc(x)
>       sin(x);
>   end proc;
> end module:
>                                                                                 
> m1:-f1(17);
                                    sin(17)
 
>
>
> restart:
>
# Case of cyclic dependency of modules (but not of procs themselves).
# This can be problematic with either/any order of defining the procedures.
>
> m1 := module()
> export f1, f3;
>   f1 := proc(x)
>     use m2 in
>       f2(x);
>     end use;
>   end proc;
>   f3 := proc(x)
>     sin(x);
>   end proc;
> end module:
Error, `m2` is not a module or member
>
> m2 := module()
> export f2;
>   f2 := proc(x)
>     use m1 in
>       f3(x);
>     end use;
>   end proc;
> end module:
Error, `m1` is not a module or member
>
>
> restart:
>
# The explicit routine-by-routine long-form of `use` works.
>
> m1 := module()
> export f1, f3;
>   f1 := proc(x)
>     use f2=:-m2:-f2 in
>       f2(x);
>     end use;
>   end proc;
>   f3 := proc(x)
>     sin(x);
>   end proc;
> end module:
>                                                                                 
> m2 := module()
> export f2;
>   f2 := proc(x)
>     use f3=:-m1:-f3 in
>       f3(x);
>     end use;
>   end proc;
> end module:
>
> m1:-f1(17);
                                    sin(17)
 
>
>
> restart:
>
# :- without `use` also works.
>
> m1 := module()
> export f1, f3;
>   f1 := proc(x)
>       m2:-f2(x);
>   end proc;
>   f3 := proc(x)
>       sin(x);
>   end proc;
> end module:
>                                                                                 
> m2 := module()
> export f2;
>   f2 := proc(x)
>       m1:-f3(x);
>   end proc;
> end module:
>
> m1:-f1(17);
                                    sin(17)