From b0ab4b99b45f32855058467ad554f7304efdea07 Mon Sep 17 00:00:00 2001
From: "Tamas K. Papp" <tkpapp@gmail.com>
Date: Thu, 5 Apr 2018 10:00:37 +0200
Subject: [PATCH] Add Fix1 (partial application).

Also add some trivial tests, and clarify that this is for two-argument
functions in the docstrings.
---
 base/operators.jl | 23 ++++++++++++++++++++---
 test/operators.jl |  9 +++++++++
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/base/operators.jl b/base/operators.jl
index 1600da1b73078..8cfb5e3f55ac9 100644
--- a/base/operators.jl
+++ b/base/operators.jl
@@ -813,12 +813,29 @@ julia> filter(!isalpha, str)
 """
 !(f::Function) = (x...)->!f(x...)
 
+"""
+    Fix1(f, x)
+
+A type representing a partially-applied version of the two-argument function
+`f`, with the first argument fixed to the value "x". In other words,
+`Fix1(f, x)` behaves similarly to `y->f(x, y)`.
+"""
+struct Fix1{F,T} <: Function
+    f::F
+    x::T
+
+    Fix1(f::F, x::T) where {F,T} = new{F,T}(f, x)
+    Fix1(f::Type{F}, x::T) where {F,T} = new{Type{F},T}(f, x)
+end
+
+(f::Fix1)(y) = f.f(f.x, y)
+
 """
     Fix2(f, x)
 
-A type representing a partially-applied version of function `f`, with the second
-argument fixed to the value "x".
-In other words, `Fix2(f, x)` behaves similarly to `y->f(y, x)`.
+A type representing a partially-applied version of the two-argument function
+`f`, with the second argument fixed to the value "x". In other words,
+`Fix2(f, x)` behaves similarly to `y->f(y, x)`.
 """
 struct Fix2{F,T} <: Function
     f::F
diff --git a/test/operators.jl b/test/operators.jl
index ea6db5cac49f1..10631fceef978 100644
--- a/test/operators.jl
+++ b/test/operators.jl
@@ -181,3 +181,12 @@ end
 
     @test fldmod1(4.0, 3) == fldmod1(4, 3)
 end
+
+@testset "Fix12" begin
+    x = 9
+    y = 7.0
+    fx = Base.Fix1(/, x)
+    fy = Base.Fix2(/, y)
+    @test fx(y) == x / y
+    @test fy(x) == x / y
+end