A combinator is a function or operator that only refers to its arguments and operands without modifying them in any way.
Symbol APL expression Bird(1) TinyAPL Diagram

I

\mathrm I

I y Identity ⊣/⊢

K

\mathrm K

K x Kestrel ⊣

κ

\kappa

κ y Kite ⊢

W

\mathrm W

W y F y Warbler ⍨

C

\mathrm C

C y F x Cardinal ⍨

B

\mathrm B

B F (G y) Bluebird ∘/⍤/⍥

Q

\mathrm Q

Q G (F y) Queer ⍛

B
1

{\mathrm B}_1

B1​ F (x G y) Blackbird ⍤

Ψ

\Psi

Ψ (G x) F (G y) Psi ⍥

S

\mathrm S

S y F (G y) Starling ⟜/⇽

Σ

\Sigma

Σ (F y) G y Violet Starling ⊸/⇾

D

\mathrm D

D x F (G y) Dove ∘/⟜

Δ

\Delta

Δ (F x) G y Zebra Dove ⍛/⊸

Φ

\Phi

Φ (F y) G (H y) Phoenix «»

Φ
1

\Phi_1

Φ1​ (x F y) G (x H y) Pheasant «»

D
2

{\mathrm D}_2

D2​ (F x) G (H y) Dovekie ⊸ + ⟜

P

\mathrm P

P (y G x) F (x G y) Parrot(2) ⸚

N

\mathrm N

N x F (x G y) Eastern Nicator ⇽

ν

\mathrm \nu

ν (x F y) G y Western Nicator ⇾
Additionally, some other primitives have combinator-like behavior:
APL expression TinyAPL Diagram n ⍨ n ⍨ F y ⁖ x G y ⁖

Footnotes

Some combinators have bird names, originating from To Mock a Mockingbird by Raymond Smullyan. Some of the bird names are taken from the Uiua combinator page.

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