[rubyrescue]

i believe that there is also a full node in Erlang, so it's not the first functional language client per the blog post. still, very cool!

[lightlike]

Also in Haskell: https://github.com/haskoin/haskoin

[xkarga00]

From their README:

   Features: 
   * [...]
   * Headerchain implementation (Blockchain with headers only)
   * [...]

This makes Haskoin more of an SPV client rather than a full-node client.

[xkarga00]

There is this repository[1] but I am not sure of its proper functionality plus it hasn't been updated for a long time.

[1] https://github.com/r-willis/biten