Solve in Standard Meta Language of New Jersey (SML) and use only recursive defin

Question

Solve in Standard Meta Language of New Jersey (SML) and use only recursive definitions built up from the basic built-in functions.!

Write a function firstN that takes a list and an int n and returns the first n elements in the list. The type of firstN should be string 'a list -> int -> 'a list. If the input list is empty or if the length of the list is less than n, then the function should return the complete list. (You may assume that n is greater than 0.)

Examples:

> firstN ["a", "b", "c", "x", "y"] 3

["a", "b", "c"]

> firstN [1,2,3,4,5,6,7] 4

[1,2,3,4]

> firstN [1,2,3,4,5,6,7] 10

[1,2,3,4,5,6,7]

> firstN [[1,2,3],[4,5],[6],[],[7,8],[]] 4

[[1,2,3],[4,5],[6],[]]

> firstN [] 5 /*may give a warning*/

[]

Explanation / Answer

fun firstN n [] = [] | firstN 0 L = [] | firstN n (x::rest) = (x::(firstN (n - 1) rest));

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