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Today's Topics:
1. about kind of (->) (Song Zhang)
2. Re: about kind of (->) (Ertugrul S?ylemez)
3. IO - getContents - putStrLn (Robert Heum?ller)
4. Re: IO - getContents - putStrLn (Tobias Brandt)
5. Re: IO - getContents - putStrLn (Michael Orlitzky)
6. Re: IO - getContents - putStrLn (Brandon Allbery)
7. Simplify (normalize) symbolic polynom-like expression
(Daniel Hlynskyi)
8. Re: Simplify (normalize) symbolic polynom-like expression
(M?t? Kov?cs)
9. problem with type (miro)
----------------------------------------------------------------------
Message: 1
Date: Sat, 16 Jun 2012 22:25:08 +0800
From: Song Zhang <[email protected]>
Subject: [Haskell-beginners] about kind of (->)
To: [email protected]
Message-ID:
<CACGMEOk6Xcn8J+4KhU1fKh=qyu8t-kebp0j7fo-0x-n9t-l...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
a function has also a kind. According to haskell report 2010 4.1.2 it is *
-> * -> *, which is easy to understand. However in ghci I type :k (->). the
output is ?? -> ? -> *. I want to know what do ?? and ? mean. Thanks
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Message: 2
Date: Sat, 16 Jun 2012 16:43:10 +0200
From: Ertugrul S?ylemez <[email protected]>
Subject: Re: [Haskell-beginners] about kind of (->)
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset="us-ascii"
Song Zhang <[email protected]> wrote:
> a function has also a kind. According to haskell report 2010 4.1.2 it
> is * -> * -> *, which is easy to understand. However in ghci I type :k
> (->). the output is ?? -> ? -> *. I want to know what do ?? and ?
> mean. Thanks
This has to do with primitive types like Int#. It basically says that
the input type can be a primitive type, and if it is, then the output
type must also be primitive.
In fact since GHC 7.4 (or perhaps earlier) the kind is
* -> * -> *
as expected.
Greets,
Ertugrul
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Message: 3
Date: Sat, 16 Jun 2012 20:03:36 +0200
From: Robert Heum?ller <[email protected]>
Subject: [Haskell-beginners] IO - getContents - putStrLn
To: [email protected]
Message-ID: <20120616200336.7bd388cd@thor>
Content-Type: text/plain; charset=US-ASCII
Hi,
this is probably an easy question, but i simply can't figure out, why
this does not work:
import Data.Char
main = do
contents <- getContents
putStrLn $ show $ splitcomma contents
splitcomma = split ','
split :: Char -> String -> [String]
split _ "" = [""]
split sp (c:cs)
| c == sp = "": rest
| otherwise = (c : head rest) : tail rest
where
rest = split sp cs
The program compiles and runs without any problems. But there is
absolutely no output, when f.eg. i type "hello, world" and hit return.
Why would that be?
Thank you very much
------------------------------
Message: 4
Date: Sat, 16 Jun 2012 20:10:01 +0200
From: Tobias Brandt <[email protected]>
Subject: Re: [Haskell-beginners] IO - getContents - putStrLn
To: Robert Heum?ller <[email protected]>
Cc: [email protected]
Message-ID:
<caoowqir7cubjgtwmcixpf9lrm6hrb6zb0gbgivebtt-esqi...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
On 16 June 2012 20:03, Robert Heum?ller <[email protected]> wrote:
> The program compiles and runs without any problems. But there is
> absolutely no output, when f.eg. i type "hello, world" and hit return.
> Why would that be?
getContents reads the entire input to the program. Under Linux
you can terminate input with Ctrl-D. If you want to only read
a single line, use getLine.
------------------------------
Message: 5
Date: Sat, 16 Jun 2012 14:10:55 -0400
From: Michael Orlitzky <[email protected]>
Subject: Re: [Haskell-beginners] IO - getContents - putStrLn
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1
On 06/16/12 14:03, Robert Heum?ller wrote:
> Hi,
>
> this is probably an easy question, but i simply can't figure out, why
> this does not work:
>
> ...
>
> The program compiles and runs without any problems. But there is
> absolutely no output, when f.eg. i type "hello, world" and hit return.
> Why would that be?
>
"Return" doesn't end the input. Try Control-D, which should work on
Linux at least (it send end-of-file).
$ runhaskell test.hs
hello, world
<ctrl+d>
["hello"," world\n"]
------------------------------
Message: 6
Date: Sat, 16 Jun 2012 14:24:56 -0400
From: Brandon Allbery <[email protected]>
Subject: Re: [Haskell-beginners] IO - getContents - putStrLn
To: Robert Heum?ller <[email protected]>
Cc: [email protected]
Message-ID:
<CAKFCL4VS0d9dBqcM-TDH=t5o2e+33_nf7zkyhpwihtvvpo-...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
On Sat, Jun 16, 2012 at 2:03 PM, Robert Heum?ller <[email protected]> wrote:
> The program compiles and runs without any problems. But there is
> absolutely no output, when f.eg. i type "hello, world" and hit return.
> Why would that be?
>
At a guess, your "split" is too strict and requires the entire input in
order to do anything, so you'd need control-D on Unix or control-Z on
Windows to mark the end of the input stream.
You might prefer to use the functions from the "split" package on Hackage
(cabal install split) which are appropriately lazy.
--
brandon s allbery [email protected]
wandering unix systems administrator (available) (412) 475-9364 vm/sms
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Message: 7
Date: Sun, 17 Jun 2012 00:17:11 +0300
From: Daniel Hlynskyi <[email protected]>
Subject: [Haskell-beginners] Simplify (normalize) symbolic
polynom-like expression
To: [email protected]
Message-ID:
<canzg+yfl6vbdq5wu80icj5cawssvkwr4xz8q62xyt0r_opj...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Hello.
I am new to typefull programming, so I've got a question.
I have a simple mathematical expression (addition, product and
exponentiation only):
> data Expr =?I Int -- integer constant
> ? ? ? ? ? | V -- symbolic variable
> ? ? ? ? ? | Sum [Expr]
> ? ? ? ? ? | Prod [Expr]
> ? ? ? ? ? | Pow Expr Expr
What I want is normalize\simplify this expression. Eg `Prod [Pow V (I
0), Pow V (I 1)] ` must be simplified to just `V`. What techniques
should I use to write `normalize` function?
Simplification rules are quite simple:
> normalize (Sum [a]) = normalize a
> normalize (Sum xs) | (I 0) `elem` xs = map nomalize . Sum $ filter (/= I 0) xs
> ? ? ? ? ? ? ? ? ? ? ? ? ?| otherwise = map normalize xs
> normalize (Prod xs) | (I 0) `elem` xs = I 0
> normalize (Prod xs) | (I 1) `elem` xs = map nomalize . Prod $ filter (/= I 1)
> xs
> ? ? ? ? ? ? ? ? ? ? ? ? ?| otherwise = map normalize xs
> normalize (Pow a (I 0)) = I 1
> normalize (Pow a (I 1)) = normalize a
and so on. But rules like theese cannot simplify some expressions, for
example, `Prod [Pow V (I 0), Pow V (I 1)] `.
------------------------------
Message: 8
Date: Sat, 16 Jun 2012 15:36:38 -0700
From: M?t? Kov?cs <[email protected]>
Subject: Re: [Haskell-beginners] Simplify (normalize) symbolic
polynom-like expression
To: Daniel Hlynskyi <[email protected]>
Cc: [email protected]
Message-ID:
<CAK4MsdrmLYhqnPoGsZbuXQ=rundwbnjcwksu4ng12cbf0zy...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Hi Daniel,
It depends on what you want to use the normalized / canonical form for.
If it's to reduce semantic equivalence testing to simple syntactic
equality, e.g.
(A == B) = (canonize(A) == canonize(B)),
then you could just use the fully expanded form, which isn't really
simplification. :)
I'm doing something similar here (for polynomial expressions over an
inner product space):
https://github.com/mkovacs/ipoly/blob/master/Poly.hs
Cheers,
M?t?
On Sat, Jun 16, 2012 at 2:17 PM, Daniel Hlynskyi <[email protected]> wrote:
> Hello.
>
> I am new to typefull programming, so I've got a question.
> I have a simple mathematical expression (addition, product and
> exponentiation only):
>
>> data Expr =?I Int -- integer constant
>> ? ? ? ? ? | V -- symbolic variable
>> ? ? ? ? ? | Sum [Expr]
>> ? ? ? ? ? | Prod [Expr]
>> ? ? ? ? ? | Pow Expr Expr
>
> What I want is normalize\simplify this expression. Eg `Prod [Pow V (I
> 0), Pow V (I 1)] ` must be simplified to just `V`. What techniques
> should I use to write `normalize` function?
> Simplification rules are quite simple:
>
>> normalize (Sum [a]) = normalize a
>> normalize (Sum xs) | (I 0) `elem` xs = map nomalize . Sum $ filter (/= I 0)
>> xs
>> ? ? ? ? ? ? ? ? ? ? ? ? ?| otherwise = map normalize xs
>> normalize (Prod xs) | (I 0) `elem` xs = I 0
>> normalize (Prod xs) | (I 1) `elem` xs = map nomalize . Prod $ filter (/= I
>> 1) xs
>> ? ? ? ? ? ? ? ? ? ? ? ? ?| otherwise = map normalize xs
>> normalize (Pow a (I 0)) = I 1
>> normalize (Pow a (I 1)) = normalize a
>
> and so on. But rules like theese cannot simplify some expressions, for
> example, `Prod [Pow V (I 0), Pow V (I 1)] `.
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
------------------------------
Message: 9
Date: Sun, 17 Jun 2012 02:39:51 +0200
From: miro <[email protected]>
Subject: [Haskell-beginners] problem with type
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"
Am a bit stuck here,... please, what is wrong with this?
checkNode :: String -> [String] -> Bool
checkNode s nodes =
[s == node | node <- nodes ]
src/me.hs:3:4:
Couldn't match expected type `Bool' with actual type `[t0]'
[1 of 1] Compiling Main ( src/me.hs, interpreted )
In the expression: [s == node | node <- nodes]
Failed, modules loaded: none.
In an equation for `checkNode':
checkNode s nodes = [s == node | node <- nodes]
thanks,
Miro
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