First-class functions/Use numbers analogously/Go interface type

This is almost the same as the code on the main page except that the "empty interface" (interface{}) has been dropped in favour of a newly defined interface type and a pair of simple implementations of that interface.

This is perhaps more idiomatic and gives better compile time type checking with no run-time panics but it possibly "hides" the "first-class function" aspect of the task. <lang go>package main

import "fmt"

func main() { var ( x Float = 2 xi Float = .5 y Float = 4 yi Float = .25 z FloatFn = func() float64 { return float64(x + y) } zi FloatFn = func() float64 { return 1 / float64(x+y) } ) // point A

numbers := []Number{&x, &y, z} inverses := []Number{&xi, &yi, zi} // point B

mfs := make([]FloatFnArg, len(numbers)) for i := range mfs { mfs[i] = multiplier(numbers[i], inverses[i]) } // pointC

for _, mf := range mfs { fmt.Println(mf(1)) } }

func multiplier(n1, n2 Number) FloatFnArg { return func(m float64) float64 { // close on interface objects n1, n2, and m return n1.Value() * n2.Value() * m } }

type Float float64 type FloatFn func() float64 type FloatFnArg func(float64) float64

func (f Float) Value() float64 { return float64(f) } func (fn FloatFn) Value() float64 { return fn() }

type Number interface { Value() float64 }</lang>