[Caml-list] Really confused - repost

[Caml-list] Really confused - repost

[Ryan Bastic]

Hey all,
  Just reread my initial message and realized how incomprehensible it
was.

  Basically, what I'm trying to do is on display at:
http://malander.undrgnd.net/foobar/students.ml

  it should be fairly clear what i'm trying to do... i want to split up
the vector
of student names into varying-sized groups, preferably using arrays of
arrays, but any other data structure will do :-) 

if you try executing students.ml, you'll see on line 68 there is a
problem...

can anyone point me in the direction as to what's going on??

Thanks
-Ryan

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Re: [Caml-list] Really confused - repost

[Matt Gushee]

On Thu, Apr 03, 2003 at 07:57:08PM -0500, Ryan Bastic wrote:
> 
>   it should be fairly clear what i'm trying to do... i want to split up
> the vector
> of student names into varying-sized groups, preferably using arrays of
> arrays, but any other data structure will do :-) 
> 
> if you try executing students.ml, you'll see on line 68 there is a
> problem...
> 
> can anyone point me in the direction as to what's going on??

Sure. What you are doing here

    !groups.(!q) := ar;

is trying to assign an array ref as the *value* of a ref. In other
words, you're trying to replace something like:

    [|"Phred","Sue"|]

with

    { contents = [|"Karla","Hans"|] }

which is obviously a different type ( string array ref instead of string
array). I think what you want to do is
    
    !groups.(!q) <- ar;

The revised version is replacing an array element (which is a ref) with
a new ref.

-- 
Matt Gushee                 When a nation follows the Way,
Englewood, Colorado, USA    Horses bear manure through
mgushee@havenrock.com           its fields;
http://www.havenrock.com/   When a nation ignores the Way,
                            Horses bear soldiers through
                                its streets.
                                
                            --Lao Tzu (Peter Merel, trans.)

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Re: [Caml-list] Really confused - repost

[Karl Zilles]

Ryan Bastic wrote:
> Hey all,
>   Just reread my initial message and realized how incomprehensible it
> was.
> 
>   Basically, what I'm trying to do is on display at:
> http://malander.undrgnd.net/foobar/students.ml
> 
>   it should be fairly clear what i'm trying to do... i want to split up
> the vector > of student names into varying-sized groups, 

It looks like all your groups are the same size.

 >preferably using arrays of
> arrays, but any other data structure will do :-) 
> 
> if you try executing students.ml, you'll see on line 68 there is a
> problem...
> 
> can anyone point me in the direction as to what's going on??

In any case, this looks like a homework assignment, so I'll just give 
you some general advice.

1) Please use descriptive variable names.   Instead of calling a binding 
"x" you might use "number_of_groups".  Everyone will love you.

2) Not everything has to be a reference.  If it doesn't change once it 
is assigned, then a simple let statement will do.

e.g.

let number_of_students = Array.length students in
let group_size = int_of_string (readline ()) in
let number_of_groups =(number_of_students + group_size - 1)/group_size in

etc...

3) Arrays are mutable.  You don't need to make arrays of references in 
order to change the contents of an array.

let tmp = Array.make 1 "" in
let groups = Array.make number_of_groups tmp in

...

let ar = Array.make !group_size "" in

..

groups.(!current_group) <- ar;

4) We're programming in a functional language.  I can tell you've 
learned C.  Those are the bad old days.

If you want to iterate over all the students, you should use:

Array.iter (fun student ->
	do something here;
   ) students;

instead of:

	let n = Array.length students - 1 in
	let i = ref 0 in
	while !i <> n do
		do something here with students.(!i);
	done;

Not only because it's shorter, but because you're less likely to make a 
mistake (hint, hint).  If you need then array index, look at the iteri 
function.


Good Luck!


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Re: [Caml-list] Really confused - repost

[Karl Zilles]

Karl Zilles wrote:
> In any case, this looks like a homework assignment, so I'll just give 
> you some general advice.

5) You can write

printf "something here"
instead of
fprintf stdout "something here"

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