[clean-list] Serious bug in the type system

[Cristian Baboi]

module t
import StdEnv

ohoh :: *{#Char} -> ( {#Char}, {#Char} )

ohoh arr #! arr1=arr
	 #! arr2=(update arr 0 'a')
	 =(arr1, arr2)

Start = ohoh "xyz"

The above return the same result.


On Sat, 15 Dec 2007 15:10:23 +0200, Edsko de Vries <devriese at cs.tcd.ie>  
wrote:

> Hi,
>
> I was working on the background section to my thesis and was exploring  
> how the
> single-threaded polymorphic lambda calculus deals with strict  
> application, and
> how this cannot really be properly dealt with in uniquenes typing or  
> linear
> logic (we need some hacks to make it work). This got me thinking about  
> exactly
> which hacks we need, and it turns out that the mechanism that is used in  
> Clean
> is not good enough! The following program is referentially opaque (not
> referentially transparent) *but passes the typechecker*:
>
>   module t
>
>   import StdEnv
>
>   ohoh :: *{#Char} -> *(*{#Char}, {#Char})
>   ohoh arr
>       #! arr` = arr
>       = (update arr 0 'a', arr`)
>  Start = ohoh {'x', 'y', 'z'}
>
> The output of this program is
>
>   ("ayz", "ayz")
>
> Edsko
> _______________________________________________
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> clean-list at science.ru.nl
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>
>
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