This lab should help you get your bearings in the WinHugs environment, learn your way around the text editor and exercise a few basic aspects of Haskell.
As with all labs, you should try to get your work done during lab hours (for most help) or on your own (e.g., at home). When you have the lab finished, you should "demo" it for me (in lab or office hours) so we can discuss your approach, problems you ran into, etc. Make sure I "check you off" as having finished the lab by the end of the demo!
Here are some simple exploratory exercises that you should be able to do based on what you've seen in lecture and the textbook.
(Note: some of these are more "research/exploratory" questions, aimed at getting you to look around the Haskell documentation sites, etc., rather than to specifically write a program.)
For the lab, choose at least seven of the following eleven exercises to demo!
same3) which compares
three different values to see if they are all the same. In other words,
when applied to the numbers 2, 3 and 4, it should return False, but when
applied to 4, (2+2) and (2*2), it should return True.
poly which evaluates the polynomial
given by 3x2 + 5x - 7. In other words, a function
which, when applied to a number, will return the value of the formula above
for that value of x.
nor
which returns True when neither of its arguments ("neither one nor
the other") is True. In all other cases it should return False.
**", "^^" and "^" in Haskell?
(hint: consider typings, but also try a few sample arguments; use the "
:t" command to find out the type of an expression,
and rememebr to put infix operators in parentheses for this purpose)
sum"
operator in Haskell? How about the "maximum" operator?
Prelude.hs": you can do this
by having only the Prelude loaded (which is the default at startup)
and then typing the ":f <function name>" command)
:s +s"),
see if you can determine a rule for how many reductions are performed when
an integer arithmetic expression with n operators is evaluated. (Express
your answer as a function of n.) For example, the expression
"2 + 3 * 5" has two operators, whereas "17 * (12 - 4) + 6 / 3"
has 4 operators.
Does the rule change if the literal values are of type Float rather than integers? (Use literals like "
4.5" to get Float values.)
twice applies its function argument
twice to a value:
twice f x = f (f x)
x" or any other variable in its place).
twice; for each
one, describe what it does in plain English. Also give an example
application and result for each.
nice = twice twice
slice = twice (twice twice)
dice = (twice twice) twice
foo = twice (take 10)
bar = twice (drop 10)
stutter which will take a number n and a
string s and return
a new string which consists of n copies of s joined together. You will
want to use the concat function (defined in the prelude) which joins
together a list of strings as follows:
> concat ["this", "is", "a", "test"]
"thisisatest"
Your function should behave as follows:
> stutter 3 "foobar"
"foobarfoobarfoobar"
(Hint: you might want to check out the Prelude function called replicate!)
stammer which will take a number n and a
string s and return
a new string which consists of all the characters from s, in order,
but with each one repeated n times. You may
want to use the map function (as defined in the prelude and demo'ed
in lecture). Remember also that a string is really just a list
of characters.
Your function should behave as follows:
> stammer 3 "foobar"
"fffoooooobbbaaarrr"
(Hint: you might want to check out the Prelude function called replicate!)