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Add Fix1 (partial application). #26708

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Apr 5, 2018
Merged

Add Fix1 (partial application). #26708

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23 changes: 20 additions & 3 deletions base/operators.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -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
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9 changes: 9 additions & 0 deletions test/operators.jl
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Expand Up @@ -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