Calculating-with-Functions

Description

Solutions

Julia

using Test


"""
返回一个闭包
"""

#> "返回一个闭包\n"

function ClosureFactory(x)
    # 此处不能写成匿名函数的形式，因为匿名函数没有默认参数
    closure(f=nothing) = isnothing(f) ? x : f(x) # return a closure
end

#> ClosureFactory (generic function with 1 method)

methods(ClosureFactory(-2))

#> # 2 methods:
#> [1] (::var"#closure#11")() in Main at none:6
#> [2] (::var"#closure#11")(f) in Main at none:6

@testset "Closure factory working tests" begin
    @test ClosureFactory(-2)() == -2
    @test ClosureFactory(-2)(abs) == 2
    @test ClosureFactory(-2)(sqrt ∘ abs) == √2
end

#> Test Summary:                 | Pass  Total
#> Closure factory working tests |    3      3

#> Test.DefaultTestSet("Closure factory working tests", Any[], 3, false, false)

# 10 data closures
zero, one, two, three, four, five, six, seven, eight, nine = map(ClosureFactory, 0:9)

#> 10-element Vector{var"#closure#11"{Int64}}:
#>  (::var"#closure#11"{Int64}) (generic function with 2 methods)
#>  (::var"#closure#11"{Int64}) (generic function with 2 methods)
#>  (::var"#closure#11"{Int64}) (generic function with 2 methods)
#>  (::var"#closure#11"{Int64}) (generic function with 2 methods)
#>  (::var"#closure#11"{Int64}) (generic function with 2 methods)
#>  (::var"#closure#11"{Int64}) (generic function with 2 methods)
#>  (::var"#closure#11"{Int64}) (generic function with 2 methods)
#>  (::var"#closure#11"{Int64}) (generic function with 2 methods)
#>  (::var"#closure#11"{Int64}) (generic function with 2 methods)
#>  (::var"#closure#11"{Int64}) (generic function with 2 methods)

# 4 operator closure factories
plus(k) = x -> x + k

#> plus (generic function with 1 method)

minus(k) = x -> x - k

#> minus (generic function with 1 method)

times(k) = x -> x * k

#> times (generic function with 1 method)

dividedBy(k) = x -> x / k

#> dividedBy (generic function with 1 method)

@testset "Fuctional Programming tests" begin
    @test eight(minus(three())) == 5
    @test seven(times(five())) == 35
end

#> Test Summary:               | Pass  Total
#> Fuctional Programming tests |    2      2

#> Test.DefaultTestSet("Fuctional Programming tests", Any[], 2, false, false)

JavaScript

const closureFactory = x => (f => f === undefined ? x : f(x));

const [zero, one, two, three, four, five, six, seven, eight, nine] =
    [0, 1, 2, 3, 4, 5, 6, 7, 8, 9].map(closureFactory);


const plus = k => (x => x + k);
const minus = k => (x => x - k);
const times = k => (x => x * k);
const dividedBy = k => (x => (x - x % k) / k);

console.log(eight(minus(three())));
console.log(seven(times(five())));

#> 5
#> 35