As Adam already said D on Pi is adventurous.
For MongoDB and web stuff, you should look into Vibe.d [0]. For
parsing I would suggest Pegged [1].
Welcome to D and Happy Hacking! :)
[0] http://vibed.org/
[1] https://github.com/PhilippeSigaud/Pegged
Thanks both. Well after several hours of hacking I have
spectacularly failed to build GDC on any arm based debian
environment - tried both my RPi and Cubieboard. In both cases it
fails with a pile of compilation errors.
I'm guessing that D just isn't mainstream enough at the moment to
be properly supported on Debian and yet it's too big and
complicated to build easily yourself and so it's probably a
non-starter for me at the moment. There is a pre-built package on
debian gdc-4.4 but it's too old to build vibe or dub from my
experimentation.
I guess I'll go back to plain old C.
Thanks anyway - I'll check back in a few years.