node to node copy

[Martin Wierich]

Hello world,

Erik Zuurbier wrote, that he needs a function for making a copy of
an array.
  I once wrote the function "CopyArray". It uses another function 
"whileU_nu".
  "whileU_nu" is a "unique" analogon to the "while"-
function in the standard environment. "whileU_nu" takes as parameters
a test-function, a transition-function and an initial value.
It performs the transition-function as long as the test function 
holds. The difference to "while" is, that the initial value is
a pair of a unique and a non-unique element. (My experience is, that
it is useful to split datastructures in that way.) 
  "CopyArray" was designed for *unboxed* arrays. It creates an array
"new" with the same size of the "original" array. Then it uses 
"whileU_nu" to copy the original array element by element into
the new array (like a "for"-loop).

CopyArray :: u:(a e) -> *(*(a e),u:(a e)) | Array a & Element e
CopyArray a
  =(aCopy,a3)
  where
    (aSize,a2)=usize a
    new=createArray aSize defaultArrayvalue
    ((a3,aCopy),_)=whileU_nu (\i->i<aSize) transfer ((a2,new),0)
    transfer ((fromm,to),i)
      =((fromm`,{to & [i]=value}),i+1)
      where
        (value,fromm`)=uselect fromm i

whileU_nu::(a -> Bool) ((.b,a) -> (.b,a)) (.b,a) -> (.b,a)
whileU_nu test step both=:(u,nu)
  | test nu=whileU_nu test step (step both)
           =both

I think, using the overloaded function "defaultArrayvalue" 
restricts the use of "CopyArray" just to unboxed arrays. For other
arrays you had to pass a value to "CopyArray", which is used to
initialize the array-elements in "createArray". So I suggest to
change the first two rows to

CopyArray :: u:(a e) -> *(*(a e),u:(a e)) | Array a
CopyArray a defaultArrayvalue

The upper version of "CopyArray" worked on Clean (1.2 I think).
Unfortunately my Clean compiler doesn't work anymore. I think
the Solaris operating system has been upgraded in my university
network, or so. I get the message "can't execute the clean-compiler".
I have made a library of many of such functions, and 
I wanted to post them to Nick Kallens repository, but I think,
I have to buy a PC first.

Let me finally ask: Why are arrays not allowed to contain
unique elements ?

greetings
  Martin Wierich (Hamburg,Germany)