WRIGHT STATE UNIVERSITY
Department of Computer Science
and Engineering
CS 776 Spring 2009 Assignment 1 (25 pts) (Due: May 1) Prasad
This problem explores the logic of the UNIX ls command, which displays the file names in the current directory. Write a list-function unixLs in SML that takes as input a list of strings, sorts them in lexicographical order and then outputs it in a tabular form. Note that you will need to experiment with the ls command, to glean the algorithm it uses to generate "squarish'' tabular outputs. The number of columns in the table output by ls depends on the length of the longest file name and the number of files, for a given window width.
One of the advantages of functional languages is the ability to write
high-level functions which capture general patterns. In this exercise, we
explore a high-level function to support list abstractions. The language Miranda
allows the user to write list abstractions of the form:
[f(x) | x <- startlist; cond(x)]
where startlist is a list of type
'a, f : 'a -> 'b (for some type
'b), and
cond : 'a ->
bool. This expression results in a list containing all elements of the
form f(x), where x
is an element in the list, "startlist", and "cond(x)"
is true. For example, if
sqr(x) = x*x and
odd(x) is true iff
x is an odd integer, then
[sqr(x) | x <- [1,2,5,4,3]; odd(x)]
returns the list [1,25,9] (that is, the squares of the odd elements of the list - 1,5,3). Note that the list returned preserves the order of startlist.
You are to write a function
listcomp : ('a -> 'b) -> ('a list)
-> ('a -> bool) -> ('b list)
in SML
so that
listcomp f startlist cond = [f(x) |
x <- startlist; cond(x)].
Consider the following definition of fast exponentiation
using recursive doubling scheme.
fun fastexp base power =
if power = 0
then 1
else if power
= 1 then base
else let val
pmod2 = power mod 2
val pdiv2 = power div 2
in
let
val auxprod = (fastexp (base * base) pdiv2)
in
if pmod2 = 0 then auxprod else base * auxprod
end
end;
Define a function countMul in SML that computes the number of multiplications
performed for various input values.
- List.tabulate (10, fn n =>
countMul 2 n);
val it = [0,0,1,2,2,3,3,4,3,4] : int list
Rewrite the above definitions in Haskell.
How to turnin the solution?
Name your solution files asg1.sml and asg1.hs and submit it electronically on unixapps1.wright.edu by executing the following command. Note that sample test cases, and documentation should be included as comments in the turned-in files.
tcsh% /common/public/tkprasad/cs776/turnin-pa1 asg1.sml asg1.hs