https://mlochbaum.github.io/BQN/doc/birds.html

(github) / BQN / doc

BQN for birdwatchers

There's now a paper (download) on this topic! Wild!

Some people consider it reasonable to name combinators after types of
birds. They make lists like the Ornithodex or Lahteenmaki's
comprehensive Combinator birds (naturally, there's a list for these
lists). There is something wrong with these people. Some of these
birds are not even real. "Quixotic bird"? Have you not heard of a
quail? Nonetheless, I don't judge such afflicted souls (certainly not
publicly), and have provided this translation table to explain BQN in
terms they can understand.

 BQN   Bird 1    1     Bird 2            2
  [?]   Identity I      Kestrel   K
  [?]   Identity I      Kite      KI
  [?]   Bluebird B      Blackbird B1
  *   Bluebird B      Psi       ps
  .   Kestrel  K                KK
  [?]            B1CBSC Queer     Q
  [?]   Starling S      ~Dove     D-like: labcd.ac(bd)
  ~   Warbler  W      Cardinal  C
k G H Dove     D      Eagle     E
F G H Phoenix  Ph      Pheasant  Ph1

Lambda calculus doesn't have BQN's polymorphism on one or two
arguments, so each BQN combinator corresponds to two lambda calculus
forms depending on the number of arguments, giving the two columns of
birds above.

Inputs are mapped to lambda calculus arguments according to the
ordering FGwx, and GFH for a 3-train F G H. For example, when I write
that the combination w F~ x corresponds to a call of C or labc.acb, a
is F and bc are wx.

Bird enthusiast Conor Hoekstra now claims what he originally mistook
for a "Golden Eagle" is in fact a Pheasant. Announced in that paper
mentioned at the top, the new identification is based on Haskell
Curry's use of Ph1 for the combinator in a 1931 paper.