Dear Stefano,

I just came across the flap code and found it can not compile since not standard conforming:
the function set_extension is declared with the elemental prefix.
But the function result is defined as allocatable which appears to be forbidden according to the fortran-standard (e.g. recent draft of f2008,f2015). A function with an allocatable function result must not be declared elemental.

Also I found that in the case of a matching file-extension the set_extension function result is not getting allocated. Not sure about the intention here: but maybe in case of matching extension newfilename should be assigned the original filename, e.g. like:
if(...)
:
else
newfilename = filename
endif

I apreciate your work anyway.
cheers
Gilbert