[clean-list] Bugs in StdOverloadedList

[Shivkumar Chandrasekaran]

I tried to use Zip and Unzip from StdOverloadedList hoping to get the  
following uniqueness propagation functionalities:

Zip :: !(!.(l a),.(l .b)) -> .(l .(a,.b)) | List l a & List l b &  
List l (a,b)
Unzip:: !.(l .(a,.b)) -> .(.(l a),.(l .b)) | List l a & List l b &  
List l (a,b)

However using Zip and Unzip in this form was rejected by the  
compiler. Ominously I noticed the following lines in  
StdOverloadedList.icl:

//Unzip:: !.(l (.a,.b)) -> (.(l .a),.(l .b)) | List l a & List l b &  
List l (a,b)	// compiler bug ?
//Unzip :: !.(a (.b,.c)) -> (.(d .b),.(e .c)) | List a (b,c) & List e  
c & List d b	// compiler bug ?

I am not sure if the implementation in StdOverloadedList.icl is a  
type inference bug or not. But I know that the following definitions  
are being accepted by Clean 2.2 (Mac OS X).

myUnzip :: !.[!.(l,.e)!] -> .([!l!], .[!.e!])
myUnzip [! !] = ([! !], [! !])
myUnzip [! (x,y) : xys !]
	#! (x1s, y1s) = myUnzip xys
	= ([! x : x1s !], [! y : y1s! ])

myZip :: !.(![!l!], !.[!.e!]) -> .[!.(l,.e)!]
myZip ([!l:ls!], [!e:es!])
	#! les = myZip (ls, es)
	= [!(l,e): les!]
myZip (_, _) = [!!]

Maybe one of the Clean gurus can comment on this, and if possible,  
implement a more generic Zip and Unzip? Thanks,

--shiv--