Function composition for multiple functions (JuliaLang/julia#33568)

Author: tkf

README.md

@@ -69,6 +69,9 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 ## Other changes
 
+* Function composition now supports multiple functions: `∘(f, g, h) = f ∘ g ∘ h`
+  and splatting `∘(fs...)` for composing an iterable collection of functions ([#33568]).
+
 ## New types
 
 ## Developer tips
@@ -127,3 +130,4 @@ includes this fix. Find the minimum version from there.
 [#29749]: https://github.com/JuliaLang/julia/issues/29749
 [#32628]: https://github.com/JuliaLang/julia/issues/32628
 [#33129]: https://github.com/JuliaLang/julia/issues/33129
+[#33568]: https://github.com/JuliaLang/julia/pull/33568

src/Compat.jl

@@ -88,6 +88,11 @@ if VERSION < v"1.3.0-alpha.8"
     Base.mod(i::Integer, r::AbstractUnitRange{<:Integer}) = mod(i-first(r), length(r)) + first(r)
 end
 
+# https://github.com/JuliaLang/julia/pull/33568
+if VERSION < v"1.4.0-DEV.329"
+    Base.:∘(f, g, h...) = ∘(f ∘ g, h...)
+end
+
 include("deprecated.jl")
 
 end # module Compat

test/runtests.jl

@@ -90,4 +90,11 @@ end
     @test_throws DivideError mod(3, 1:0)
 end
 
+# https://github.com/JuliaLang/julia/pull/33568
+@testset "function composition" begin
+    @test ∘(x -> x-2, x -> x-3, x -> x+5)(7) == 7
+    fs = [x -> x[1:2], uppercase, lowercase]
+    @test ∘(fs...)("ABC") == "AB"
+end
+
 nothing