Adding sugar - map, reduce and filter, etc to slice

package main

import "fmt"

type MyList []string // a custom type can be a builtin type if you want it to be

func (ml MyList) Filter(f func(string) bool) []string {
    na := []string{}
    for _, v := range ml {
        if add := f(v); add {
            na = append(na, v)
        }
    }
    return na
}

func (ml MyList) Reduce(f func(prev, current string, index int) string) []string {
    na := []string{}
    for i, v := range ml {
        if i == 0 {
            na = append(na, f("", v, i))
        } else {
            na = append(na, f(ml[i-1], v, i))
        }
    }
    return na
}

func (ml MyList) Map(f func(val string) *string) []string {
    na := []string{}
    for _, v := range ml {
        mVal := f(v)
        if nil != mVal {
            na = append(na, *mVal)
        }
    }
    return na
}

//Lets try them out
func main() {
    list := MyList{"test", "test2"}
    fList := list.Filter(func(v string) bool {
        if v == "test" {
            return true
        }
        return false
    })
    fmt.Println(fList)

    rList := list.Reduce(func(prev, current string, index int) string {
        return fmt.Sprintf("%s%s:%d", prev, current, index)
    })
    fmt.Println(rList)

    mList := list.Map(func(val string) *string {
            val = val + " I WAS MAPPED"
            return &val
        return nil
    })
    fmt.Println(mList)
}