Re: [Haskell-cafe] Re: ANNOUNCE: deepseq-1.0.0.0
On 18/11/2009 04:05, Malcolm Wallace wrote: The documentation claim that The default implementation of 'deepseq' is simply 'seq' is not exactly right, as `deepseq` and `seq` have different signatures. Yes indeed. In order to use deepseq, it looks like I also need some way to force the () return value, e.g. let res = deepseq (my big computation) in res `seq` use res or let res = deepseq (my big computation) in case res of () - use res or let !res = deepseq (my big computation) in use res Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANNOUNCE: deepseq-1.0.0.0
Hello Simon, Wednesday, November 18, 2009, 12:17:31 PM, you wrote: You could argue that (a - b - b) is doing more than (a - ()), if i correctly understand, we have two versions: 1) easier to use 2) more efficient and one of them may be defined via another? how about providing both versions, with simpler name for simpler version? -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANNOUNCE: deepseq-1.0.0.0
On Wed, 2009-11-18 at 09:17 +, Simon Marlow wrote: So the main difference is that with the current formulation of deepseq, you need to explicitly force the result in order to use it, either with a pattern match, another seq, or a pseq. If we used (a - b - b) then the top-level forcing is built-in. Let's look at an example instance; here (1) is the current deepseq, (2) is deepseq :: a - b - b instance (DeepSeq a, DeepSeq b) = DeepSeq (a,b) where -- (1) deepseq (a,b) = deepseq a `seq` deepseq b -- (2) deepseq (a,b) = deepseq a . deepseq b They're both fairly similar. Most instances follow this pattern, with seq being replaced by (.). You could argue that (a - b - b) is doing more than (a - ()), because it has a kind of built-in continuation (Luke's point). I buy that, although (a - ()) has a strange-looking unit type in the result and you have to use it in conjunction with seq. I think the most important thing is to make the public interface that people use most frequently simple and easy to remember. Thus I suggest the primary function people use should be deepseq :: DeepSeq a = a - b - b because then all that users have to remember is: deepseq --- like seq but more so! That's it. Users already know how to use seq, so now they know how to use deepseq too. (1) generates slightly better code with GHC, because it compiles seq directly into a case expression, whereas (.) involves a thunk. If deepseq is inlined all the way down, then it would turn into the same thing either way. I don't feel terribly strongly, but I have a slight preference for the current version. If it so happens that it is more convenient or faster to make the class and instances use the (a - ()) style then that is fine. We can give the class method a different name. Presumably people have to write Deepseq instances much less frequently than they use deepseq. Duncan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANNOUNCE: deepseq-1.0.0.0
On Tue, Nov 17, 2009 at 8:48 PM, Dean Herington heringtonla...@mindspring.com wrote: The documentation claim that The default implementation of 'deepseq' is simply 'seq' is not exactly right, as `deepseq` and `seq` have different signatures. Which raises the more interesting question: Why did you choose a different signature? And, would a version of `seq` with the same signature as `deepseq` be useful? The situation is analogous to, say, null having this signature: null :: [a] - Bool Instead of this one: null :: [a] - b - b - b Or the recent famous debate about returning Maybe a vs. Monad m = m a for failure. If we have seq' :: a - (), then we have seq = m . seq' where m () = id And of course we can go the other way too. So it is a question of taste. deepseq is simpler by at least two standards: it is not polymorphic and it has only one argument. There are exactly two values of both () and forall b. b - b, but that fact is more obvious of the former (IMO). I think it is the right choice. Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANNOUNCE: deepseq-1.0.0.0
The documentation claim that The default implementation of 'deepseq' is simply 'seq' is not exactly right, as `deepseq` and `seq` have different signatures. Yes indeed. In order to use deepseq, it looks like I also need some way to force the () return value, e.g. let res = deepseq (my big computation) in res `seq` use res or let res = deepseq (my big computation) in case res of () - use res I suppose the advantage of this approach is to ensure that the user must let-bind the forced value to a name. A beginner might write (my big computation) `seq` use (my big computation) without realising that it fails to do what they desire. Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
