On 10/02/2012 03:22, Donn Cave wrote:
modifyRecord :: RecordType r = (a - a) - (r - a) - r - r
data Config { tempo :: Int, ...}
f = modifyRecord tempo (+20)
I'm hoping I missed something, and that you don't intend the (r - a)
part of this in particular to be taken literally.
On 07/02/2012 22:56, Richard O'Keefe wrote:
On 8/02/2012, at 2:11 AM, Steve Horne wrote:
To be fair, field OF record isn't bad in that sense. However, it would defeat
the purpose of TDNR - the record isn't first, and therefore cannot be used (given a
left-to-right typing direction
On 06/02/2012 23:58, Richard O'Keefe wrote:
On 4/02/2012, at 12:13 AM, Gábor Lehel wrote:
All of this said, record.field is still the most readable, intuitive,
and familiar syntax for selecting a field from a record that I know
of.
Having learned COBOL and Algol 68 before Haskell was dreamed
On 04/02/2012 08:46, MigMit wrote:
Well, if you want that in production, not for debugging purposes, you should
change the type signature of mergesort so that it uses some monad. Printing
requires IO monad; however, I would advise to collect all intermediate results
using Writer monad, and
On 03/02/2012 11:13, Gábor Lehel wrote:
The first problem is that mixing prefix and postfix function
application within the same line makes it harder to read. When you
read code to try to understand what it does, the direction you like to
go in is here's some object, first do this to it, then do
On 30/01/2012 07:09, Donn Cave wrote:
((separate . crack . .smallEnd) egg).yolk
(f egg).yolk where f = separate . crack . .smallEnd
Scary - that .smallEnd worries me. It's like a field is being
referenced with some magical context from nowhere.
Obviously I need to read that full proposal.
On 28/01/2012 13:00, Paul R wrote:
AntC Steve, I think that proposal has been rather superseeded by
AntC http://hackage.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields,
which
AntC draws on TDNR. But SORF is best seen as an evolving design space, with
precise
AntC details yet to be
On 30/01/2012 04:23, Steve Horne wrote:
On 28/01/2012 13:00, Paul R wrote:
AntC Steve, I think that proposal has been rather superseeded by
AntC
http://hackage.haskell.org/trac/ghc/wiki/Records/OverloadedRecordFields,
which
AntC draws on TDNR. But SORF is best seen as an evolving design
On 25/01/2012 16:13, R J wrote:
hello Haskell the holidays are coming up soon and I think this can help
http://www.news13open.com
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There's a proposal at the moment to add support for TDNR to Haskell - to
leverage the power of the dot (e.g. for intellisense).
http://hackage.haskell.org/trac/haskell-prime/wiki/TypeDirectedNameResolution
I approve of the goal, but I'd like to suggest a different approach.
My basic idea is
On 21/01/2012 17:29, Victor S. Miller wrote:
The do notation translates
do {x- a;f} into
a=(\x - f)
However when we're working in the IO monad the semantics we want requires that
the lambda expression be strict in its argument. So is this a special case for
IO? If I wanted this behavior
On 21/01/2012 18:08, Steve Horne wrote:
Even so, to see that strictness isn't the issue, imagine that (=)
were rewritten using a unary executeActionAndExtractResult function.
You could easily rewrite your lamba to contain this expression in
place of x, without actually evaluating
On 11/01/2012 15:20, Thomas Schilling wrote:
Based on your stated background, the best start would be the (longer)
paper on the Spineless Tagless G-machine [1].
Thanks for the tips. I haven't read much yet, but considering [1], I
guess I shouldn't have dismissed SPJs early 90's stuff so
Although I'm far from being an expert Haskell programmer, I think I'm
ready to look into some of the details of how it's compiled. I've a copy
of Modern Compiler Design (Grune, Bal, Jacobs and Langendoen) - I first
learned a lot of lexical and parsing stuff from it quite a few years
ago.
On 08/01/2012 20:25, Brent Yorgey wrote:
On Fri, Jan 06, 2012 at 10:51:58AM +, Steve Horne wrote:
If I specify both extensions (-XMultiParamTypeClasses and
-XFlexibleInstances) it seems to work, but needing two language
extensions is a pretty strong hint that I'm doing it the wrong way
On 08/01/2012 21:13, Brandon Allbery wrote:
(Also, de facto I think it's already more or less been decided in
favor of type families, just because functional dependencies are (a) a
bit alien [being a glob of Prolog-style logic language imported into
the middle of System Fc] and (b) [as I
On 07/01/2012 12:17, Christoph Breitkopf wrote:
Hello,
I wonder why Data.Map provides the indexed access functions:
http://hackage.haskell.org/packages/archive/containers/latest/doc/html/Data-Map.html#g:21
These functions seem rather out-of-place to me in the map api. The
only use case I
I was messing around with type-classes (familiarization exercises) when
I hit a probably newbie problem. Reducing it to the simplest case...
module BinTree ( WalkableBinTree, BT (Branch, Empty) ) where
-- n : node type
-- d : data item type wrapped in each node
class WalkableBinTree n
On 06/01/2012 10:29, Steffen Schuldenzucker wrote:
On 01/06/2012 11:16 AM, Steve Horne wrote:
I was messing around with type-classes (familiarization exercises) when
I hit a probably newbie problem. Reducing it to the simplest case...
module BinTree ( WalkableBinTree, BT (Branch, Empty
On 06/01/2012 10:39, Jon Fairbairn wrote:
groupBy is currently implemented using span. It strikes me that we
ought to specify some properties for what we want. Start by defining:
pairwiseInOrderBy p l = all (uncurry p) (l `zip` drop 1 l) giving all
(pairwiseInOrderBy p) (groupCut p l) and we
On 05/01/2012 10:02, Jon Fairbairn wrote:
Steve Hornesh006d3...@blueyonder.co.uk writes:
Personally, I think this is a tad disappointing. Given that
groupBy cannot check or enforce that it's test respects
equivalence classes, it should ideally give results that
make as much sense as possible
On 05/01/2012 11:09, Brandon Allbery wrote:
On Thu, Jan 5, 2012 at 05:57, Steve Horne sh006d3...@blueyonder.co.uk
mailto:sh006d3...@blueyonder.co.uk wrote:
-- groupCut - Similar to groupBy, but where groupBy assumes an
equivalence relation,
-- groupCut takes a function
On 05/01/2012 11:55, Christian Maeder wrote:
Am 05.01.2012 11:57, schrieb Steve Horne:
[...]
groupCut :: (x - x - Bool) - [x] - [[x]]
[...]
How about a break function that respects an escape character (1. arg)
(and drops the delimiter - 2. arg) and use this function for unfolding
On 02/01/2012 11:12, Jon Fairbairn wrote:
maxm...@mtw.ru writes:
I want to write a function whose behavior is as follows:
foo string1\nstring2\r\nstring3\nstring4 = [string1,
string2\r\nstring3, string4]
Note the sequence \r\n, which is ignored. How can I do this?
cabal install split
then
On 04/01/2012 16:47, Steve Horne wrote:
(a == a)
reflexivity : (a == b) = (b == a)
transitivity : (a == b) (b == c) = (a == c)
Oops - that's...
reflexivity : (a == a)
symmetry : (a == b) = (b == a)
transitivity : (a == b) (b == c) = (a == c)
An equivalence relation is a relation
On 02/01/2012 06:12, Arseniy Alekseyev wrote:
I don't know what to actually do with this after putting it in a *.lhs file.
You can :load *.lhs into ghci the same way you load .hs-files.
I swear I tried this before, but now it suddenly works.
Must be the chaos of stupid random assumptions
On 02/01/2012 09:44, max wrote:
I want to write a function whose behavior is as follows:
foo string1\nstring2\r\nstring3\nstring4 = [string1,
string2\r\nstring3, string4]
Note the sequence \r\n, which is ignored. How can I do this?
Doing it probably the hard way (and getting it wrong) looks
On 02/01/2012 10:03, Jerzy Karczmarczuk wrote:
But I disagree quite strongly with the idea of /World parameter as
purely hypothetical, a trick used to gain an intuition/. I mentioned
the language Clean (no reaction, seems that Haskellians continue to
ignore it...)
I don't know about others,
On 01/01/2012 22:57, Jerzy Karczmarczuk wrote:
Dan Doel :
...
Also, the embedded IO language does not have this property.
do x- m ; f x x
is different from
do x- m ; y- m ; f x y
and so on. This is why you shouldn't write your whole program with IO
functions; it lacks nice
I'm having another go at figuring out Monad Transformers, starting at
the same point I've started and stopped the last couple of times. That's
this tutorial...
http://blog.sigfpe.com/2006/05/grok-haskell-monad-transformers.html
Onion layers, lift etc - I get that. But I've never actually got
On 31/12/2011 13:18, Yves Parès wrote:
But still, I maintain my previous view. I could clarify that by saying
that (e.g. for Maybe) we could separate it in two types, Maybe itself
and its monad:
-- The plain Maybe type
data Maybe a = Just a | Nothing
-- The MaybeMonad
newtype MaybeMonad a =
On 30/12/2011 10:41, Bardur Arantsson wrote:
This doesn't sound right to me. To me, a side effect is something
which happens as a (intended or unintended) consequence of something
else. An effect which you want to happen (e.g. by calling a procedure,
or letting the GHC runtime interpreting
On 30/12/2011 15:23, Gregg Reynolds wrote:
Now one way of understanding all this is to say that it implicates the
static/dynamic (compile-time/run-time) distinction: you don't know what e.g. IO
values are until runtime, so this distinction is critical to distinguishing
between pure and
On 30/12/2011 15:50, Gregg Reynolds wrote:
On Dec 30, 2011, at 10:34 AM, Artyom Kazak wrote:
Gregg Reynoldsd...@mobileink.com писал(а) в своём письме Fri, 30 Dec 2011
17:23:20 +0200:
Regarding side-effects, they can be (informally) defined pretty simply: any
non-computational effect
On 30/12/2011 10:47, Bardur Arantsson wrote:
On 12/29/2011 11:06 PM, Steve Horne wrote:
Using similar mixed definitions to conclude that every C program is full
of bugs (basically equating intentional effects with side-effects, then
equating side-effects with unintentional bugs) is a fairly
On 30/12/2011 20:38, Scott Turner wrote:
On 2011-12-30 14:32, Steve Horne wrote:
A possible way to implement a Haskell program would be...
1. Apply rewrite rules to evaluate everything possible without
executing primitive IO actions.
2. Wait until you need to run the program.
3
On 29/12/2011 08:48, Heinrich Apfelmus wrote:
Steve Horne wrote:
Heinrich Apfelmus wrote:
Purity has nothing to do with the question of whether you can
express IO in Haskell or not.
The beauty of the IO monad is that it doesn't change anything about
purity. Applying the function
On 29/12/2011 18:04, Donn Cave wrote:
Quoth Steve Hornesh006d3...@blueyonder.co.uk,
...
Anyway, if you're using IO actions, your code is not referentially
transparent and is therefore impure - by your own definition of
impure. Causing side-effects may not be pedantically the issue, but
the mix
On 29/12/2011 18:41, Chris Smith wrote:
Entering tutorial mode here...
On Thu, 2011-12-29 at 10:04 -0800, Donn Cave wrote:
We can talk endlessly about what your external/execution results
might be for some IO action, but at the formulaic level of a Haskell
program it's a simple function value,
On 29/12/2011 19:21, Heinrich Apfelmus wrote:
Why would IO Int be something special or mysterious? It's an
ordinary value like everything else; it's on the same footing as
[Char], Maybe Int, Int - String, Bool, and so on. I see no difference
between the list [1,2,3] :: [Int] and the
side effects,
why not call - let x = whatever in Something - also a local
side-effect?
Oh, that you can often transform let in the application of lambda,
thus purely functional?
Doesn't matter, Steve Horne will explain you that (sorry for the
irony): let is a compile-time pure construct
On 29/12/2011 19:26, Heinrich Apfelmus wrote:
Steve Horne wrote:
Heinrich Apfelmus wrote:
Again, purity refers to the semantics of functions (at run-time):
given the same argument, will a function always return the same
result? The answer to this question solely decides whether
On 29/12/2011 19:55, Bardur Arantsson wrote:
On 12/29/2011 08:47 PM, Steve Horne wrote:
On 29/12/2011 19:21, Heinrich Apfelmus wrote:
BTW - why use an IO action for random number generation? There's a
perfectly good pure generator. It's probably handy to treat it
monadically to sequence
On 29/12/2011 20:39, Jerzy Karczmarczuk wrote:
Still, I dont understand what does S.H. mean by a perfectly good
pure generator.
Tell more please (unless you just mean a stream, say:
Probably bad wording, to be honest. I only meant that there's random
number handling support in the Haskell
On 29/12/2011 21:01, Chris Smith wrote:
On Thu, 2011-12-29 at 18:07 +, Steve Horne wrote:
By definition, an intentional effect is a side-effect. To me, it's by
deceptive redefinition - and a lot of arguments rely on mixing
definitions - but nonetheless the jargon meaning is correct within
On 29/12/2011 21:51, Jerzy Karczmarczuk wrote:
Steve Horne :
I only meant that there's random number handling support in the
Haskell library and, and least judging by type signatures, it's pure
functional code with no hint of the IO monad.
Look well at those functions, please.
Challenge
On 30/12/2011 00:16, Sebastien Zany wrote:
Steve Horne wrote:
I haven't seen this view explicitly articulated anywhere before
See Conal Elliott's blog post The C language is purely functional
http://conal.net/blog/posts/the-c-language-is-purely-functional.
Thanks - yes, that's basically
On 29/12/2011 23:30, Chris Smith wrote:
Sorry to cut most of this out, but I'm trying to focus on the central
point here.
On Thu, 2011-12-29 at 22:01 +, Steve Horne wrote:
In pure functional terms, the result should be equivalent to a fully
evaluated value - but putStrLn isn't pure
On 30/12/2011 00:22, Jerzy Karczmarczuk wrote:
Steve Horne :
Some code (intended to be loaded into GHCi and played with)
-- import System.Random
-- randSelect this is a list 5 (mkStdGen 9877087)
-- ...
module P23 (randSelect) where
-- ...
randSelect' (x:xs) n l g
I've been for functions like GetMessage, TranslateMessage and
DispatchMessage in the Haskell Platform Win32 library - the usual
message loop stuff - and not finding them. Hoogle says no results found.
Is this level of Win32 GUI coding supported? (other than by dealing with
the FFI myself)
On 30/12/2011 01:37, Chris Smith wrote:
On Fri, 2011-12-30 at 00:44 +, Steve Horne wrote:
So, to resurrect an example from earlier...
f :: Int - IO Int
f = getAnIntFromTheUser= \i - return (i+1)
Did you mean f :: IO Int ? If not, then I perhaps don't understand
your example, and your
On 30/12/2011 01:40, Scott Turner wrote:
On 2011-12-29 19:44, Steve Horne wrote:
[Interaction with its environment] is as much an aspect of what
Haskell defines as the functional core.
Switching mental models doesn't change the logic
But it does. Other languages do not support the distinction
On 30/12/2011 03:43, Chris Wong wrote:
On Fri, Dec 30, 2011 at 2:53 PM, Steve Horne
sh006d3...@blueyonder.co.uk wrote:
I've been for functions like GetMessage, TranslateMessage and
DispatchMessage in the Haskell Platform Win32 library - the usual message
loop stuff - and not finding them
On 30/12/2011 04:07, Chris Smith wrote:
On Fri, 2011-12-30 at 01:53 +, Steve Horne wrote:
I've been for functions like GetMessage, TranslateMessage and
DispatchMessage in the Haskell Platform Win32 library - the usual
message loop stuff - and not finding them. Hoogle says no results found
This is just my view on whether Haskell is pure, being offered up for
criticism. I haven't seen this view explicitly articulated anywhere
before, but it does seem to be implicit in a lot of explanations - in
particular the description of Monads in SBCs Tackling the Awkward
Squad. I'm entirely
On 28/12/2011 20:44, Heinrich Apfelmus wrote:
Steve Horne wrote:
This is just my view on whether Haskell is pure, being offered up for
criticism. I haven't seen this view explicitly articulated anywhere
before, but it does seem to be implicit in a lot of explanations - in
particular
On 28/12/2011 22:01, Jerzy Karczmarczuk wrote:
Le 28/12/2011 22:45, Steve Horne a écrit :
Yes - AT COMPILE TIME by the principle of referential transparency it
always returns the same action. However, the whole point of that
action is that it might potentially be executed (with potentially
On 28/12/2011 23:56, Bernie Pope wrote:
On 29 December 2011 10:51, Steve Hornesh006d3...@blueyonder.co.uk wrote:
As Simon Baron-Cohen says in Tackling the Awkward Squad...
I think you've mixed up your Simons; that should be Simon Peyton Jones.
Oops - sorry about that.
FWIW - I'm diagnosed
Sorry for the delay. I've written a couple of long replies already, and
both times when I'd finished deleting all the stupid stuff there was
nothing left - it seems I'm so focussed on my own view, I'm struggling
with anything else today. Maybe a third try...
On 28/12/2011 19:38, AUGER Cédric
On 29/12/2011 00:57, Thiago Negri wrote:
We can do functional programming on Java. We use all the design
patterns for that.
At the very end, everything is just some noisy, hairy,
side-effectfull, gotofull machinery code.
The beauty of Haskell is that it allows you to limit the things you
need
On 29/12/2011 01:53, Antoine Latter wrote:
The beauty of the IO monad is that it doesn't change anything about
purity. Applying the function
bar :: Int - IO Int
to the value 2 will always give the same result:
Yes - AT COMPILE TIME by the principle of referential transparency it always
On haskell.org, the 2011.4.0.0 version is shown as the current stable
release - but the most recent download link is for the 2011.2.0.0 version.
This is bugging me a little because the documentation in the 2011.2
Haskell Platform download for Windows is broken - there's at least one
bug
On 27/12/2011 18:36, Bas van Dijk wrote:
On 27 December 2011 19:13, Steve Hornesh006d3...@blueyonder.co.uk wrote:
On haskell.org, the 2011.4.0.0 version is shown as the current stable
release - but the most recent download link is for the 2011.2.0.0 version.
What download link are you
On 27/12/2011 18:57, Steve Horne wrote:
OK - I really should have tried that before. But... why would an old
page hang around in my Firefox cache so long and not get updated? I've
not had this on any other sites.
I still should be doing more checking before posting.
A look in the source
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