Re: [Haskell-cafe] handling read exceptions
S. Alexander Jacobson wrote: My point is that I am reading in name/value pairs and once I know the name, I know the type of the value, but I don't want to have to pass that information programatically to the point in the code where I am doing the read. OK, I see... I don't know the exact syntax you are using (e.g. how are the strings terminated?), but reads is still useful: readIS :: ReadS (Either Integer String) readIS s = take 1 $ [ (Left x, t) | (x, t) - reads s ] ++ [ (Right x, t) | (x, t) - lex s ] Then we have: Main readIS 123blah [(Left 123,blah)] Main readIS blah123 [(Right blah123,)] Main readIS [(Right ,)] Main readIS foo bar [(Right foo, bar)] If you have only simple parsing tasks and are not looking for extreme performance, the Read class is a good choice. Otherwise you should probably have a look at the Parsec package which comes with Hugs and GHC: http://www.haskell.org/ghc/docs/latest/html/libraries/parsec/Text.ParserCombinators.Parsec.html or Happy: http://haskell.org/happy/ Cheers, S. ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Building Haddock on Windows
Yes, I suspect you have a mismatch between the version of Haddock on your system and the version of Haddock used to produce the interfaces. Try upgrading GHC. Cheers, Simon -Original Message- From: Bayley, Alistair [mailto:[EMAIL PROTECTED] Sent: 05 April 2004 16:19 To: Simon Marlow Cc: [EMAIL PROTECTED] Subject: RE: [Haskell-cafe] Building Haddock on Windows Trying to invoke Haddock with --read-interface=c:\ghc\ghc-6.0\doc\html\base\base.haddock Initially I get a stack overflow, so I added: +RTS -K2M -RTS ... and now I get: Fail: end of file Action: Data.Binary.getWord8 Is the --read-interface option specified correctly? This is where my GHC installation is, and the base.haddock file exists in there. I assume this is the interface file. Is this a compatibility problem? i.e. haddock file distributed with GHC 6.0 too old for Haddock 0.6? -Original Message- From: Simon Marlow [mailto:[EMAIL PROTECTED] Sent: 17 March 2004 15:29 To: Bayley, Alistair Cc: [EMAIL PROTECTED] Subject: RE: [Haskell-cafe] Building Haddock on Windows - why doesn't it know what Int, String, Float, IO, Monad, Show, etc are? What invocation option do I need to ensure it links to Prelude/hierarchical-library stuff? (I think it's --read-interface; must I generate interface files for the Prelude and libraries though?) You get the interfaces for the libraries with a GHC installation. Just use the --read-interface flag to tell Haddock about them. Cheers, Simon - * Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. * ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] What's wrong with my Haskell code?
when loading the following code, hugs escaped and reported that
ERROR cal24.hs:10 - Instance of Integral (Ratio Integer) required for
definition of Main.eval
I don't know why and how to solve it, anyone help me?
data ETree = Add ETree ETree
| Sub ETree ETree
| Mul ETree ETree
| Div ETree ETree
| Node Integer
deriving Show
eval :: ETree-Maybe Rational
eval (Node x)= Just (fromInteger x)
eval (Add t1 t2) = do { x-eval t1; y-eval t2;
if x=y then return (x+y) else Nothing }
eval (Sub t1 t2) = do { x-eval t1; y-eval t2; return (x-y) }
eval (Mul t1 t2) = do { x-eval t1; y-eval t2;
if x=y then return (x*y) else Nothing }
eval (Div t1 t2) = do { x-eval t1; y-eval t2;
if y/=0 then return (x `div` y) else Nothing }
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Re: [Haskell-cafe] What's wrong with my Haskell code?
It is because you use 'div' instead of '/'.
div :: Integral a = a - a - a
(/) :: Fractional a = a - a - a
Rationals are instance of the class Fractional, but not of Integral
Prelude :i Fractional
class Num a = Fractional a where
(/) :: a - a - a
recip :: a - a
fromRational :: Rational - a
fromDouble :: Double - a
-- instances:
instance Fractional Float
instance Fractional Double
instance Integral a = Fractional (Ratio a)
Hope this helps,
Arthur
On 13-apr-04, at 20:44, Meihui Fan wrote:
when loading the following code, hugs escaped and reported that
ERROR cal24.hs:10 - Instance of Integral (Ratio Integer) required
for definition of Main.eval
I don't know why and how to solve it, anyone help me?
data ETree = Add ETree ETree
| Sub ETree ETree
| Mul ETree ETree
| Div ETree ETree
| Node Integer
deriving Show
eval :: ETree-Maybe Rational
eval (Node x)= Just (fromInteger x)
eval (Add t1 t2) = do { x-eval t1; y-eval t2;
if x=y then return (x+y) else Nothing }
eval (Sub t1 t2) = do { x-eval t1; y-eval t2; return (x-y) }
eval (Mul t1 t2) = do { x-eval t1; y-eval t2;
if x=y then return (x*y) else Nothing }
eval (Div t1 t2) = do { x-eval t1; y-eval t2;
if y/=0 then return (x `div` y) else Nothing }
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RE: [Haskell-cafe] Building Haddock on Windows
Try upgrading GHC. Thanks, I'll try that. Would it be too much to ask that Haddock be distributed with GHC? Reasons for: - GHC library docs are produced with Haddock - GHC library docs already include Haddock interface files - would ensure version of Haddock matches that used to produce interface files - would save lazy developers like myself from downloading and compiling. Think of it as one less barrier to overcome; a small step closer to more widespread adoption. Reasons against: - would favour one documentation tool over others - would add an unnecessary item to GHC build/packaging procedure (is this much of an overhead?) Mind you, if you include Haddock, why stop there? Why not include other developers tools, like (say) Hmake, Happy, Hat, ...? Alistair. -Original Message- From: Simon Marlow [mailto:[EMAIL PROTECTED] Sent: 13 April 2004 10:59 To: Bayley, Alistair Cc: [EMAIL PROTECTED] Subject: RE: [Haskell-cafe] Building Haddock on Windows Yes, I suspect you have a mismatch between the version of Haddock on your system and the version of Haddock used to produce the interfaces. Try upgrading GHC. Cheers, Simon -Original Message- From: Bayley, Alistair [mailto:[EMAIL PROTECTED] Sent: 05 April 2004 16:19 To: Simon Marlow Cc: [EMAIL PROTECTED] Subject: RE: [Haskell-cafe] Building Haddock on Windows Trying to invoke Haddock with --read-interface=c:\ghc\ghc-6.0\doc\html\base\base.haddock Initially I get a stack overflow, so I added: +RTS -K2M -RTS ... and now I get: Fail: end of file Action: Data.Binary.getWord8 Is the --read-interface option specified correctly? This is where my GHC installation is, and the base.haddock file exists in there. I assume this is the interface file. Is this a compatibility problem? i.e. haddock file distributed with GHC 6.0 too old for Haddock 0.6? - * Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. * ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] WildCard question
Hi, I am very new to haskell and the program hugs and I am having problems using the wildcard operator _ Every time I try to use it in an definition it says something like the symbol /017 is not recognised. I am sure my defintions are correct as I tested it with an example defintion from Alan Thompsons craft of functional programming book. I am guessing that all the relevant modules havenot been loaded properly. I have reinstalled hugs with full implementation and this has not helped. I am using a windows 98 PC. Any help suggestions? Or has anyone just got the wildcard definition which are could just paste into my scripts Many thanks Yahoo! Messenger - Communicate instantly..."Ping" your friends today! Download Messenger Now___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] WildCard question
Paul Cosby [EMAIL PROTECTED] writes: Every time I try to use [underscore] in an definition it says something like the symbol /017 is not recognised Could that be \017, i.e. octal 17 (defined in ASCII as SI, whatever that may be)? Any help suggestions? Wild guess: Are your files using the same character set as your Haskell system is expecting? I know Windows pulls some occasional stunts with the character set (and occasionally lies about it), but I wasn't aware that it affected underscore. -kzm -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] C Bindings?
Does Haskell have some mechanism that allows it to link to C, or other imperative languages? I know, you could use the IO Monad to do it...using stdin and stdout as pipes to any other program. But is there a way to link Haskell into a C program? Thanks again for the help for a newbie... Russ ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] C Bindings?
Hi, The Foreign Function Interface (FFI) is your friend for these tasks: http://www.cse.unsw.edu.au/~chak/haskell/ffi/ On the haskell.org web page, under libraries and tools there are links to a number of tools to help you connect your C haskell programs. The GreenCard and c-haskell tools seem to be used by a number of people. Alastair Reid's Guide to Haskell's Foreign Function Interface, http://www.reid-consulting-uk.ltd.uk/docs/ffi.html is a good place to start. It has some comparison of the various tools. Best Wishes, Greg On Apr 13, 2004, at 12:56 PM, Russ Lewis wrote: Does Haskell have some mechanism that allows it to link to C, or other imperative languages? I know, you could use the IO Monad to do it...using stdin and stdout as pipes to any other program. But is there a way to link Haskell into a C program? Thanks again for the help for a newbie... Russ ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] C Bindings?
It's not really newbie stuff, but maybe this is what you're looking for: http://www.cse.unsw.edu.au/~chak/haskell/ffi/ #g -- At 09:56 13/04/04 -0700, Russ Lewis wrote: Does Haskell have some mechanism that allows it to link to C, or other imperative languages? I know, you could use the IO Monad to do it...using stdin and stdout as pipes to any other program. But is there a way to link Haskell into a C program? Thanks again for the help for a newbie... Russ ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe Graham Klyne For email: http://www.ninebynine.org/#Contact ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] WildCard question
On 2004-04-13 at 18:52+0200 Ketil Malde wrote: Paul Cosby [EMAIL PROTECTED] writes: Every time I try to use [underscore] in an definition it says something like the symbol /017 is not recognised Could that be \017, i.e. octal 17 (defined in ASCII as SI, whatever that may be)? SI is Shift In, if I remember correctly, not that the operation of devices like Flexowriters is of any relevance. However, I'd guess that it's hexadecimal 17, because ord '_' `rem` 16 == 15 == 0x17. So for some reason it's talking about the botom four bits of '_'! Any help suggestions? Wild guess: Are your files using the same character set as your Haskell system is expecting? I know Windows pulls some occasional stunts with the character set (and occasionally lies about it), but I wasn't aware that it affected underscore. Windows is a mystery to me, however. My guess would be something translating from one page of a character table to another. What locale are you in? Jón -- Jón Fairbairn [EMAIL PROTECTED] ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
