When I first heard that non-used modules are not imported in Ikarus
my gut reaction was negative. I saw various issues with that approach.
The first issue is that what I write is not what I get: if I write
(import (x)) I expect the module x to be imported and I do not want
the compiler to lie to me.
The second issue is that a programmer reading the import line will
assume that something comes from module x (even if the module is not
actually used) and will waste time studying module x before realizing
that all of its exported bindings are not used.
Importing a module which is not used 99% of the times is a consequence
of refactoring: the dependency was used in the first version of the
script, or was used during development, and you forgot to drop it from
the import list. This happens to me all the time in Python, and I
solve the issue by using pylint, a tool that warns me about unused
modules.
In general, I think the right thing to do with unused modules is to
print a compiler warning and to import them anyway.
If you silently ignore unused modules, and people rely on this
feature, the risk is to litter many programs with unused imports
which will just confuse your readers.
Finally, there the issue of modules which are just imported for
side effects. This happens 1% of the times, is tricky, I did not think
of it and I realized only yesterday the consequences (basically, it
makes it harder to use Matthew Flatt's trick to manage side-effects
at compile time).
On this point I do not have a clear mind (do I want to rely on side
effects at compile time across modules?). However, the previous
points stand out: the compiler should do as I ask and instantiate a module,
even if the only thing the module does is to print a debugging message.
Curious to know what others think of this issue,
Michele Simionato
