collect.go

package main

import "fmt"

func collect(vals []int, f func(int) int) []int {
	length := len(vals)
	newVals := make([]int, length, length)

	for i, val := range vals {
		newVals[i] = f(val)
	}

	return newVals
}

func main() {
	ints := []int{1, 2, 3, 4, 5}
	result := collect(ints, func (a int) int {
		return a + 1
	})
	fmt.Println(result)
}

comb.go

package main

import "fmt"

func comb(a, b func(int) int) func(int) int {
	return func(x int) int {
		return a(b(x))
	}
}

func main() {
	add1 := func(x int) int {
		return x + 1
	}

	add2 := func(x int) int {
		return x + 2
	}

	add3 := comb(add1, add2)

	fmt.Println(add3(4))
}

partial.go

package main

import "fmt"

func partial(f func(int, int) int, a int) func(int) int {
	return func(x int) int {
		return f(a, x)
	}
}

func main() {
	add := func(a, b int) int {
		return a + b
	}

	add4 := partial(add, 4)
	fmt.Println(add4(2))
}

reduce.go

package main

import "fmt"

func reduce(vals []int, init int, f func(int, int) int) int {
	result := init

	for _, val := range vals {
		result = f(result, val)
	}

	return result
}

func main() {
	ints := []int{1, 2, 3, 4, 5}
	result := reduce(ints, 0, func (sum, i int) int {
		return sum + i
	})
	fmt.Println(result)
}