Andy Georges wrote:

Hi Kaoru,

...

I have been working through the exercises in Thompson's The Craft of Functional Programming 2nd Ed book. I am looking for a solution web site for Thompson's book. Or maybe the people here can help.

In exercise 4.4, I am asked to define a function

howManyOfFourEqual :: Int -> Int -> Int -> Int -> Int

which returns the number of integers that are equal to each other. For example,

howManyOfFourEqual 1 1 1 1 = 4 howManyOfFourEqual 1 2 3 1 = 2 howManyOfFourEqual 1 2 3 4 = 0

A solution which is applicable to any number of arguments is this:

when this example occurs in the text the new Haskell coder has not been introduced to most of what you suggest. Some of the exercises I felt were meant to be a little painful so that when you were introduced to a new concept a chapter or two later you would think "oh, that would have made X.Y so much easier".

Date: Sat, 12 Mar 2005 23:39:21 -0800 From: Sean Perry Cc: Haskell-Cafe@haskell.org

As an aside, I kept all of the exercises in revision control. So I can look back at what I first wrote and my later changes. A habit I plan to keep as I move on to other programming texts and languages.

That's a nice approach. But I can't resist asking: once you've learned Haskell, what is there left to move on to? ;-) Mike

Date: Sun, 13 Mar 2005 00:01:17 -0800 From: Sean Perry Cc:

Michael Vanier wrote:

...

...

Date: Sat, 12 Mar 2005 23:39:21 -0800 From: Sean Perry Cc: Haskell-Cafe@haskell.org

As an aside, I kept all of the exercises in revision control. So I can look back at what I first wrote and my later changes. A habit I plan to keep as I move on to other programming texts and languages.

That's a nice approach. But I can't resist asking: once you've learned Haskell, what is there left to move on to? ;-)

(-:

I try to learn a new language every other year or so. Lisp and I have butted heads many times. So I thought I would try Haskell -- already love Python and the two are clearly siblings with divorced parents.

Unfortunately since Haskell is neither C nor Perl, I will probably only dabble in it, much like Python. Not a fact I like, but one that the corporate world keeps making me swallow.

Actually, haskell and python share little except some syntactic similarities. But haskell shares a lot with lisp/scheme. There are some good books on scheme e.g. SICP (http://mitpress.mit.edu/~sicp) and "How to Design Programs" (http://www.htdp.org) which would be very helpful for the beginning haskell programmer to absorb (you have to learn to walk before you can write monadic parser combinators ;-)). OTOH lisp and scheme are strict languages, like ocaml, unlike haskell, which is lazy. That makes a big difference in practice. As for C or Perl, try using haskell to generate C or Perl and don't tell your employers where the C/perl code came from ;-) Even though I'm just a haskell newbie myself, I think it's the most interesting language around, by a pretty wide margin. Mike