Fix "implicit none" usage

[certik]

There should be exactly one implicit none in each module at the top. No function in that module should have it, as it is redundant (the module one applies to all functions in the module). I'll send a PR once #9 is in, to avoid merge conflicts.

[mandli]

Yeah, I agree that this is unnecessary. This is done for the sake of older Fortran programmers so that they are reminded that each function does not have implicit typing. Since it does not actually affect the compilation of the code and may avoid problems I tend to put that statement in every subroutine.

Or perhaps there is a reason not to put that in everywhere?

[certik]

It all depends on what culture you want to create in the project. I would assume that people will send PRs with additions, so it's easy to check that there is implicit none in each module at top. And in that case, any additional implicit none is just obstructing the code. The compiler will refuse to compile unless you specify types, so older Fortran programmers will get instantly reminded that they need to specify types. So the purpose of a reminder is served imho.

The reason not to put it everywhere is simply to keep the code short and consistent.

[mandli]

That is a good point, the compiler will inform people of their mistake before it gets too far along. Also, with the travis builds it will be easier to make sure someone does not accidentally do something and break everything.

Let's remove them.

[certik]

Note that we can go even further and write a simple Python script that checks all .f90 module files to have "implicit none" at the module level. This will then naturally fail at Travis. This script might be reusable in other Fortran projects as well. There really should be a compiler option that does this particular check, but unfortunately I am not aware of any, except -Wimplicit-interface.

Update: gfortran also has -fimplicit-none, but I would discourage using it, as other compilers might not enforce this. We need to make sure that the code itself enforces "implicit none".

[mandli]

Looks like it's not supported very widely anyway. I would say remove the implicit nones and leave them in the module section.

[certik]

Cool. I'll send a PR later.