-----Original Message-----
From: Frank Dellaert [mailto:frank@cc.gatech.edu]
Sent: 18 December 2001 11:48
To: Simon Peyton-Jones; Haskell@haskell.org
Subject: Re: space efficiency question

Thanks !

 

Now, a small follow-up question: if I subsequently test 2 Instances whether they were instantiated with the same Attributes value, as in

 

test (Instance a1 _) (Instance a2 _) = (a1==a2)

 

will this be implemented efficiently ? I.e. will it check first whether the pointers happen to be the same, and only then do a full Eq comparison ?

 

Cheers

Frank

----- Original Message -----

From: Simon Peyton-Jones

To: Frank Dellaert ; Haskell@haskell.org

Sent: Monday, December 17, 2001 10:24 AM

Subject: RE: space efficiency question

Now: if I have a couple of thousand of these Instances, created with the same Attributes value, as in:

 

a = Attributes ["a","bc"]

i0000 = Instance a [1,2]

i0001 = Instance a [1,1]

...

i7896 = Instance a [2,1]

 

can I be assured that there are not thousands of actual copies of a but that they simply have a pointer to a ? I'm interested in the answer for both ghc (compiled/interpreted) as interpreted Hugs. 

Yes for GHC: you'll only get one copy of 'a'.

 

Simon