Added docstrings and tests for compositions

base/operators.jl

@@ -332,8 +332,25 @@ eltype(x) = eltype(typeof(x))
 
 |>(x, f) = f(x)
 
+"""
+    ∘(f, g)
+    f ∘ g
+
+Creates a composition of two functions (or functor objects), such that
+`(f ∘ g)(x...) == f(g(x...))`. The `∘` symbol can be accessed at the REPL using
+`\\circ`.
+
+By default, an anonymous function `(x...) -> f(g(x))` is returned, but this may
+be specialized to create any functionally-equivalent callable object.
+"""
 ∘(f, g) = (x...)->f(g(x...))
 
+"""
+    !(f::Function)
+
+Applies boolean not to the output of `f`, return a new function
+`(x...) -> !f(x...)` such that `(!f)(x...) = !(f(x...))`.
+"""
 !(f::Function) = (x...)->!f(x...)
 
 # array shape rules

test/operators.jl

@@ -55,3 +55,6 @@ let xs = [[i:i+4;] for i in 1:10]
         @test max(xs[1:n]...) == [n:n+4;]
     end
 end
+
+@test ((x -> x+1) ∘ (x _> 2x))(5) == 11
+@test (!isless)(1,2) == false