gmane.comp.lang.haskell.hugs.user

(no subject)

Benjamin L. Russell — 2011-11-16T05:02:45

http://www.andrejschwarcz.com/wp-content/themes/andrej6/images/names.php

[ann] hugs on JVM

Szymon Jachim — 2011-04-03T20:07:38

Just a small announcement about a nice toy that I've put online.
Hugs 98 compiled to a Java class: http://code.google.com/p/jhugs/

Next step will be to run it on a Android based phone.

Another nice thing thing would be to create a JSR 223 ScriptEngine.
This would allow to script Java existing business classes with Haskell.

Szymon
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Re: the standard function enumFrom

Daniel Fischer — 2010-10-25T15:30:27

That's not a definition to be used for all cases, it's a default definition 
to be used if nothing better is provided.


Because [fromEnum A .. ] is [0 .. ], which is [0 .. maxBound :: Int] and 
the derived Enum instance calls error for arguments of toEnum outside the 
range [0 .. number of constructors - 1].


The derived Enum instance is cleverer, it uses the number of constructors 
in the datatype to determine upper bounds for enumFrom and enumFromTo, so 
that [x .. ] and [x, y .. ] don't try to call toEnum on an invalid 
argument.


No, the derived Enum instances don't use the default method (which would 
rarely be the right thing to do).

the standard function enumFrom

Paqui Lucio — 2010-10-25T15:12:45

Hi,
Given the following enumerated type (as an example)

data P = A | B | C | D | E 
         deriving (Show,Enum)

and the Prelude definition: 
     enumFrom x  = map toEnum [ fromEnum x ..]

I guess that  the two expressions 
1) (map toEnum [ fromEnum A ..]) :: [P]
2)  enumFrom A 
should produces the same result, say 
[A,B,C,D,E] :: [P] 

However, the expression 1)  produces an error as a consequence of trying to
apply toEnum to the number 5.
¿Why the expression 2) doesn't not produce the same error?
¿Does Hugs not apply the definition in the Prelude for evaluating the
expression 2)?
There should be something that I'm missing in this computation. 
Some hints?

Thanks in advance,
Paqui

--------------------------------- 
Paqui Lucio                                
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Re: RV: Hugs in Windows Seven

Neil Mitchell — 2010-10-07T22:11:47

Hi,

I see no reason for any Windows version of Hugs not working on Windows
7, but I've never tested it.

Thanks, Neil

On Wed, Oct 6, 2010 at 4:27 PM, Paqui Lucio <paqui.lucio< at >ehu.es> wrote:

RV: Hugs in Windows Seven

Paqui Lucio — 2010-10-06T15:27:09

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Re: WinHugs

Neil Mitchell — 2010-10-04T14:48:22

Hi Han-Hing,

I'm afraid I don't run WinHugs anymore, and have never run the OpenGL
portions. Perhaps someone on the Hugs user list can help?

Thanks, Neil

On Mon, Oct 4, 2010 at 12:39 PM, Han-Hing Dang
<h.dang< at >informatik.uni-augsburg.de> wrote:

unicode support

Rustom Mody — 2010-07-27T19:48:32

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Anyone have hugs version of gofer modular-interpretercode?

Larry Evans — 2010-06-30T14:46:43

Page 2 of:

http://www.cs.yale.edu/~liang-sheng/popl95.ps.gz

says the source code is at:

   nebula.cs.yale.edu/pub/yale-fp/modular-interpreter

However, that's no longer present.

Since Hugs is the successor to gofer, I was wondering
if anyone could tell me how to get a copy of the
corresponding hugs code.

TIA.

-Larry

Re: stack overflow in tail recursive function

Daniel Fischer — 2010-03-24T14:03:43

-----Ursprüngliche Nachricht-----
Von: Bruno Schneider 
Gesendet: 24.03.2010 13:56:32
An: hugs-users< at >haskell.org
Betreff: Re: [Hugs-users] stack overflow in tail recursive function



Well, the thunk is built on the heap, that's correct, but when it's evaluated, things go on the stack.


That's okay, but as a rule of thumb, if you don't know that it's
implementation-specific, haskell-cafe or beginners (depending on what
sort of answer you want) is the better choice; hugs-users or
glasgow-haskell-users are less frequented.

In this case, the behaviour is a little implementation-dependent, if you use GHC and compile with optimisations, 
the
strictness-analyser should see that the result of the multiplication is
needed and the compiler should make it strict by itself.
(I currently have no access to a computer with GHC installed, so I can't check that it does indeed.) 


Cheers,
Daniel

Re: stack overflow in tail recursive function

Bruno Schneider — 2010-03-24T12:56:32

[...]

So it goes to the stack, hum? It thought it would be just a pointer to
some computation type on the heap.

Anyway, thanks for the detailed answer. I asked here because I didn't
test that code on any other compiler/interpreter, so it could be
something related to hugs implementation.

Re: stack overflow in tail recursive function

Daniel Fischer — 2010-03-24T10:27:18

-----Ursprüngliche Nachricht-----
Von: Neil Mitchell <ndmitchell< at >gmail.com>
Gesendet: 23.03.2010 21:40:39
An: Bruno Schneider 
Betreff: Re: [Hugs-users] stack overflow in tail recursive function



Yes, this sort of general Haskell questions will receive earlier and more answers in the cafe.
Nevertheless, Neil, I'm not sure he'd get a much more detailed answer to this question there ;)

Okay, so



Laziness is more pervasive than you expected. Your accumulator doesn't actually accumulate the product so far, it accumulates the way to obtain that product, because the multiplication isn't carried out but deferred until really needed.
So the evaluation of factorial 4 goes

fat' 4 1
(4 /= 1)
fat' (4-1) (4*1)
(4-1 = 3 /= 1)
fat' (3-1) (3*(4*1))
(3-1 = 2 /= 1)
fat' (2-1) (2*(3*(4*1)))
(2-1 = 1 == 1)
(2*(3*(4*1)))

and this expression is only evaluated if necessary. factorial 20000 builds a thunk of 20000 nested multiplications, this is tried to evaluate when the value is demanded for printing, but the expression i

Re: stack overflow in tail recursive function

Neil Mitchell — 2010-03-23T20:40:39

Hi Bruno,

I suggest you ask this question on the haskell-cafe< at > mailing list -
it's a general Haskell question, and you'll get a much more detailed
answer there.

Thanks, Neil

On Tue, Mar 23, 2010 at 12:01 PM, Bruno Schneider <boschneider< at >gmail.com> wrote:

stack overflow in tail recursive function

Bruno Schneider — 2010-03-23T12:01:54

Hi all,

I have this tail recursive factorial function:

factorial :: Integer -> Integer
factorial 0 = 1
factorial n = fat' n 1 where
    fat' 1 fat = fat
    fat' n fat = fat' (n-1) (n*fat)

Whenever I run it with a number of 20000 or more I get a stack
overflow error. It doesn't seem a problem with the large resulting
number because, if so, the message should be something like "Garbage
collection fails to reclaim sufficient space". Other functions seem to
able to handle a larger number of recursive calls.

So, what is the problem with this particular function?

Re: Scoping inconsistency in ghci

Malcolm Wallace — 2009-11-24T03:47:05

The first is a qualified operator, the second is not.  The correct  
syntax to make a qualified operator prefix is (List.\\).  There has  
been some discussion of changing it in Haskell Prime to match your  
intuition for how it should look, but the change was rejected for  
H'2010.  Maybe it will be adopted in H'2011 or H'2012.


Yes, ghci is decidedly strange in this respect.  Any name from any  
exposed package is available in qualified form at the command prompt,  
without having to load the module containing it.  Indeed,  
frustratingly, ghci will often complain if you *do* try to load the  
module:

     Prelude> :l List
     <no location info>: module `List' is a package module
     Failed, modules loaded: none.

Regards,
     Malcolm

Re: Scoping inconsistency in ghci

Ahn, Ki Yung — 2009-11-24T03:45:08

Sorry this was my complete confustion (List.\\) is not same as List.(\\).

Ahn, Ki Yung 쓴 글:

Scoping inconsistency in ghci

Ahn, Ki Yung — 2009-11-24T03:37:14

Running ghci without any option or scripts to load, I've experienced
some inconsistencies prelude List.\\ and List.(\\) .  The former is in
scope, but the latter is not.  This seem strange.  My expectation is
that neither of them should be in scope unless we load the List module
with with the :m command.

I'm using Debian distribution of GHC 6.10.4, and here is an example run
of ghci to show this issue.

kyagrd< at >kyagrd:~/tmp$ ghci
GHCi, version 6.10.4: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
Prelude> [1,2,3,4] List.\\ [1,3]
[2,4]
Prelude> List.(\\) [1,2,3,4] [1,3]

<interactive>:1:0: Not in scope: data constructor `List'

<interactive>:1:5: Not in scope: `\\'
Prelude> :q
Leaving GHCi.
kyagrd< at >kyagrd:~/tmp$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.10.4
kyagrd< at >kyagrd:~/tmp$ uname -a
Linux kyagrd 2.6.30-2-686 #1 SMP Sat Sep 26 01:16:22 UTC 2009 i6

Re: the built-in function enumFrom

Daniel Fischer — 2009-10-29T11:34:10

Am Donnerstag 29 Oktober 2009 11:06:31 schrieb Paqui Lucio:

That's the default implementation, when an instance declaration doesn't provide an 
explicit method.


Of course.
[fromEnum Falsity .. ] is a list of Ints, namely [0 .. ]
(which is [0 .. maxBound :: Int]).
Mapping toEnum over that list can give a list of any type belonging to Enum, so it must 
somehow be specified which type to use (Bool, Int, Integer, (), Char, ...)


Because the implementation is smarter than the default method :)
Given a type with k constructors, the implementation will, upon a clause "deriving Enum", 
create methods enumFrom(Then) that work, probably by doing something like

enumFrom val = map toEnum [fromEnum val .. k-1]

the built-in function enumFrom

Paqui Lucio — 2009-10-29T10:06:31

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Re: Opening text editor

Neil Mitchell — 2009-10-21T20:05:08

Hi

WinHugs actually supports a few TextEditors - Textpad, Notepad and
another I can't remember (Jot rings a bell...). However, it won't
offer to use TextPad unless you have TextPad installed, and similarly
with the other editor. It's not too hard to add more editors to
WinHugs, if you have a basic knowledge of C.

You should be able to use any editor using the Custom facility.

Thanks

Neil

2009/10/13 Irfon-Kim Ahmad <irfon< at >ambienautica.com>:

Re: Opening text editor

Irfon-Kim Ahmad — 2009-10-13T19:18:17

In WinHugs, you set the editor by going to File | Options and on the 
"WinHugs" tab, there's a section called "Editor".  It's actually really 
hard to miss.

Given that the only built-in options it offers are "Notepad" and 
"Custom", it's safe to conclude that it doesn't ship with any other 
editor.  I use Programmer's Notepad 2, which is available as freeware.

Someone has posted a syntax highlighting definition set for PN2 here:

http://compsci.ca/v3/viewtopic.php?t=14630

I have not tried it myself.