Using ML (or Scheme or some “functional-algorithm-language” like ML or Scheme),

Question

Using ML (or Scheme or some “functional-algorithm-language” like ML or Scheme), define the following functions:
a) evens(X) to create a list consisting of every other element in X starting with the second one (2st, 4rd , etc.) It should return empty list if X does not have at least two items
b) last (X) to return the last value in list X
c) double (X) to double each item in list X
d) cnt (a,X) to count how many times a appears in X.
e) less (a,X) to create a list consisting of all integers in X that are less than a.

Explanation / Answer

Solution:

a)

a) evens(X) to create a list consisting of every other element in X starting with the second one (2st, 4rd , etc.) It should return empty list if X does not have at least two items

evens x | length(x) < 1 = []

               | otherwise = evens' x

evens' [] = []

evens' [a] = []

evens' (a:b:x) = b:(evens' x)

b) last (X) to return the last value in list X

lastt [] = undefined

lastt [a] = a

lastt (a:x) = lastt x

c) double (X) to double each item in list X

double1 [] = []       -- if you mean double is trepeat o each element again

double1 (a:x) = a:a:(double1 x)

double2 [] = [] -- if you mean double is to multiply each element by 2

double2 (a:x) = (2*a):(double2 x)

d) cnt (a,X) to count how many times a appears in X.

cnt a [] = 0

cnt a (v:x) | a == v = 1+(cnt a x)

                 | otherwise = cnt a x

e) less (a,X) to create a list consisting of all integers in X that are less than a.

less a [] = []

less a (v:x) | v<a = v:(less a x)

                   | otherwise = less a x

I hope this helps if you find any problem. Please comment below. Don't forget to give a thumbs up if you liked it. :)

Related Questions

Navigate

• Browse (All)
• Browse U
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.