Monads/Writer monad: Difference between revisions

=={{header|Go}}==

{{trans|Kotlin}}

<lang go>package main

import (

"fmt"

"math"

)

type mwriter struct {

value float64

log string

}

func (m mwriter) bind(f func(v float64) mwriter) mwriter {

n := f(m.value)

n.log = m.log + n.log

return n

}

func unit(v float64, s string) mwriter {

return mwriter{v, fmt.Sprintf(" %-17s: %g\n", s, v)}

}

func root(v float64) mwriter {

return unit(math.Sqrt(v), "Took square root")

}

func addOne(v float64) mwriter {

return unit(v+1, "Added one")

}

func half(v float64) mwriter {

return unit(v/2, "Divided by two")

}

func main() {

mw1 := unit(5, "Initial value")

mw2 := mw1.bind(root).bind(addOne).bind(half)

fmt.Println("The Golden Ratio is", mw2.value)

fmt.Println("\nThis was derived as follows:-")

fmt.Println(mw2.log)

}</lang>

{{out}}

<pre>

The Golden Ratio is 1.618033988749895

This was derived as follows:-

Initial value : 5

Took square root : 2.23606797749979

Added one : 3.23606797749979

Divided by two : 1.618033988749895

</pre>