/*
* Extenstion function on List to reproduce the map method
* Note need to use a name distinct from map, otherwise the already
* defined map will always take precedence
* @author gtowell
* Created: Oct 25, 2021
 */
fun <T> List<T>.mapgtM(fn: (T)->String): List<String> {
    val ret = mutableListOf<String>()
    fun irec(that:List<T>) {
        if (that.count()==0) return;
        ret.add(fn(that.get(0)))
        return irec(that.drop(1))
    }
    irec(this)
    return ret
}

fun <T> List<T>.mapgt(fn: (T)->String): List<String> {
    fun irec(that:List<T>, ret:List<String>): List<String> {
        if (that.count()==0) return ret;
        return irec(that.drop(1), ret+fn(that.get(0)))
    }
    return irec(this, emptyList<String>())
}

// for recursive function, you need to decalare the return type
// even if you use the shorthand function definition in one expression
// Doing it totally generically
fun <T,U> List<T>.mapgt2(fn: (T)->U): List<U> {
    fun irec(that:List<T>, ret:List<U>): List<U> = 
        if (that.count()==0) 
            ret 
        else 
            irec(that.drop(1), ret+fn(that.get(0)))
    
    return irec(this, emptyList<U>())
}

fun main() {
    val aa = listOf<Int>(1,2,3,4)
    val rr = aa.mapgtM({ a:Int -> "<<%s %s>>".format(a, "A")})
    println(rr)
    println(aa.mapgt({ a:Int -> "<<%s %s>>".format(a, "B")}))
    println(aa.mapgt2({ a:Int -> "<<%s %s>>".format(a, "C")}))

}