November 2001 - Hugs-Bugs

[igloo@earth.li: Strictness of library implementations]
by Ian Lynagh 14 Nov '01

14 Nov '01

Forwarded as I believe it is a hugs bug ----- Forwarded message from Ian Lynagh <igloo(a)earth.li> ----- Subject: Strictness of library implementations To: haskell(a)haskell.org From: Ian Lynagh <igloo(a)earth.li> Date: Sun, 11 Nov 2001 19:37:43 +0000 Delivered-To: haskell(a)haskell.org Errors-To: haskell-admin(a)haskell.org X-Mailman-Version: 2.0.3 The library report says The code found here is a specification, rather than an implementation. Implementations may choose more efficient versions of these functions. However, all properties of these specifications must be preserved, including strictness properties. Ratio then defines data (Integral a) => Ratio a = !a :% !a which GHC seems to implement as specified, but nhc and hugs seem to use data (Integral a) => Ratio a = a :% a Does this not have different strictness properties? Thanks Ian _______________________________________________ Haskell mailing list Haskell(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell ----- End forwarded message -----

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Problem with Win XP
by Klaus Faßbender 14 Nov '01

14 Nov '01

Hi! I used hugs with Win98 and there were no problems. But since I updated to WinXP I get this Error-Message (see the file below). I need it for studying Informatics. We´re learning Haskell and our Prof explains it with Hugs as compiler. So I hope you can help me with my problem. Klaus Faßbender

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(no subject)
by Andrew Mishchenko 14 Nov '01

14 Nov '01

Hi, there. Try something like :set +p%s%s and hugs is dead :) Of course I know what's wrong, but I can't undo anything... Druxa.

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Win 1 of 100 Naked Music NYC CDs
by OM Records 13 Nov '01

13 Nov '01

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Windows XP Bug
by Eric 08 Nov '01

08 Nov '01

I recently installed Windows XP and winhugs.exe gets a fatal error in this version of Windows. In the Hugs console it says 'ERROR: Illegal character escape sequence "\W"' and another error in a window says 'FATAL ERROR: Unable to load prelude'. However, the DOS version runs fine. Just letting you guys know about this in case you already didn't. Do you plan to release another version for XP anytime soon? Eric Cornett

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RE: Not lazy/smart enough
by Lennart Augustsson 02 Nov '01

02 Nov '01

> I think the best approach would be to throw an exception by every > computation can cannot be computed, with an additional information of what > type the problem is (like divide by zero, square root of negative, etc). > Then on top of that can build new types with the desired behavior. You can't catch exceptions locally in any suggested extension of Haskell, so this is impossible. I think it's much cleaner to keep Infinity and NaN, and then raise an exception if these value should ever occur where you cannot handle them. IEEE754 propagates the special values in a nice way so it work pretty well. That said, don't think Haskell's Float&Double are ideal for serious numerical work; you might need finer control of things like rounding modes etc. -- Lennart

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RE: Not lazy/smart enough
by Hans Aberg 02 Nov '01

02 Nov '01

At 11:17 +0100 2001/11/02, Lennart Augustsson wrote: >Are you using projective or affine infinity? At 10:26 +0000 2001/11/02, Simon Marlow wrote: >I have absolutely no idea. Which one should we be using? How do we >find out which one we are using? My guess is that by "affine infinity" Lennart means +oo/-oo, but what you are using in GHCi is what the FPU is producing, probably a NaN for every computation it cannot perform. This NaN roughly corresponds to saying that there has been an exception without specifying what it consist of (think of the exception monad!). I think the best approach would be to throw an exception by every computation can cannot be computed, with an additional information of what type the problem is (like divide by zero, square root of negative, etc). Then on top of that can build new types with the desired behavior. -- Thus, the basic floating point type should not have any infinities or such (but throw an exception, or treat NaN as a thrown exception). Hans Aberg

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RE: Not lazy/smart enough
by Lennart Augustsson 02 Nov '01

02 Nov '01

> > > because we choose to represent floating point > > > exceptions with the special values Infinity > > Are you using projective or affine infinity? > > I have absolutely no idea. Which one should we be using? How do we > find out which one we are using? If (-1)/0 is -Infinity you are using affine, if it's Infinity you are using projective. IEEE754 allows you to have both (selectable in some fashion). One is not better than the other; they are both useful. The affine completion of the number axis makes the use of -0 more comprehensible (1/(-Infinity) == -0, 1/(-0) == -Infinity). -- Lennart

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RE: Not lazy/smart enough
by Simon Marlow 02 Nov '01

02 Nov '01

> > because we choose to represent floating point > > exceptions with the special values Infinity > Are you using projective or affine infinity? I have absolutely no idea. Which one should we be using? How do we find out which one we are using? Simon

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RE: Not lazy/smart enough
by Lennart Augustsson 02 Nov '01

02 Nov '01

> because we choose to represent floating point > exceptions with the special values Infinity Are you using projective or affine infinity? -- Lennart

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