[SOLVED] CS 431 Programming language concepts Homework 4

Homework 4
1 Introduction
For this homework, you will implement some SML functions using pattern
matching.
1. Your solution should be a working ML program in a text le that I can
run on a console using command like use “hwk4.sml”;
2. You may add comments to your program such as (* Question 1 *).
3. Use `let’ expression as necessary for local variables and local functions.
2 Questions
1. Write a function zip that takes two lists and return a list of 2-tuples.
For example, zip ([1, 2, 3], [4, 5]) should return [(1,4), (2,5)].
Note that if one list is longer than the other, the unmatched portion of
the longer list is ignored.
2. Write a function unzip that takes a list of 2-tuples and return a tuple
of two lists. For example, unzip [(1,2), (3,4), (5,6)] should return
([1,3,5], [2,4,6]).
3. Write a function zip3 that takes three lists and return a list of 3-tuples.
For example, zip3 ([1, 2, 3], [4, 5], [6,7,8]) should return [(1,4,6), (2,5,7)].
Note that if one list is longer than the others, the unmatched portion of
the longer list is ignored.
4. Write a function unzip3 that takes a list of 3-tuples and return a tuple of
three lists. For example, unzip3 [(1,2,3), (4,5,6), (7,8,9)] should
return ([1,4,7], [2,5,8], [3,6,9]).
5. Write a function zipWithIndex that takes a list and return a list of 2-
tuples, where each tuple contains an index and a list element. For example,
zipWithIndex [“a”, “b”, “c”] should return [(0, “a”), (1, “b”), (2, “c”)].
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6. Write a function flatten that takes a list of lists and return a at-
tened list. For example, flatten [[1,2], [3], [4,5,6]] should return
[1,2,3,4,5,6].
7. Write a function flatten2 that takes a list of 2-tuples and return a at-
tened list. For example, flatten2 [(1,2), (3,4), (5,6)] should re-
turn [1,2,3,4,5,6].
3 Submission
Please write your solution in a text le by the name of hwk4.sml and submit it
to the dropbox.
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