Doubting Haskell

[Cale Gibbard]

On 04/03/2008, Luke Palmer <lrpalmer@...> wrote:

> On Tue, Mar 4, 2008 at 4:16 AM, Ketil Malde <ketil@...> wrote:
>  > Paul Johnson <paul@...> writes:
>  >
>  >  > I'm surprised you found the significant whitespace difficult.
>  >
>  >  I wonder if this has something to do with the editor one uses?  I use
>  >  Emacs, and just keep hitting TAB, cycling through possible alignments,
>  >  until things align sensibly.  I haven't really tried, but I can
>  >  imagine lining things up manually would be more painful, especially
>  >  if mixing tabs and spaces.
>
>
> Especially if mixing tabs and spaces indeed.  Haskell does the Python
>  thing of assuming that a tab is 8 spaces, which IMO is a mistake.  The
>  sensible thing to do if you have a whitespace-sensitive language that
>  accepts both spaces in tabs is to make them incomparable to each
>  other; i.e.

<snip>

I honestly think that tab characters occurring anywhere but in a
comment should be considered a lexical error and rejected by the
compiler outright. More problems are caused by trying to continue with
only tabs, or some mixture of tabs and spaces than just getting one's
editor to expand tabs automatically.

 - Cale
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[Evan Laforge]

> Especially if mixing tabs and spaces indeed.  Haskell does the Python
> thing of assuming that a tab is 8 spaces, which IMO is a mistake.  The

FWIW, most people in python land think the same thing, and the -t flag
makes mixed tabs and spaces a warning or error.  At the least, -Wall
could report mixed usage.  At the most, make it an error.
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[Henk-Jan van Tuyl]

About the line length needed for Haskell programs, there was a discussion
about this some time ago, that could be regarded as a tutorial for
reducing indentation:
    http://haskell.org/pipermail/haskell-cafe/2007-July/028787.html

As for the idle core you mention: I keep one core fully occupied with a
program that searches for a cure against cancer, see:
    http://www.computeagainstcancer.org/

The example you gave for the use of "map" can be simplified:
    map func (take (10 [0..]))  -- should actually be: map func (take 10
[0..])
->
    map func [0..9]

Regards,
Henk-Jan van Tuyl


--
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http://Van.Tuyl.eu/
--


On Tue, 04 Mar 2008 07:29:24 +0100, Alan Carter <alangcarter@...>
wrote:

> Many thanks for the explanations when I was first experimenting with
> Haskell. I managed to finish translating a C++ wxWidgets program into
> Haskell wxHaskell, and am certainly impressed.
>
> I've written up some reflections on my newbie experience together with
> both versions, which might be helpful to people interested in
> popularizing Haskell, at:
>
> http://the-programmers-stone.com/2008/03/04/a-first-haskell-experience/
>
> Regards,
>
> Alan
>

--
--
Met vriendelijke groet,
Henk-Jan van Tuyl


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2008/3/4, Alan Carter <alangcarter@...>:
>  I've written up some reflections on my newbie experience together with
>  both versions, which might be helpful to people interested in
>  popularizing Haskell, at:
>
>  http://the-programmers-stone.com/2008/03/04/a-first-haskell-experience/

This is truly interesting, any learning experience is enlightening, we
truly do need to lower this barrier of admittance of which you speak.

On another subject, there are still point in your code that could be
clearer or done with less              cruft :

maxOfHistogram stats = snd (foldl (\(cA, vA) (cB, vB) -> if (vA > vB)
                                                            then (cA, vA)
                                                            else (cB, vB))
                                  (0, 0)
                                  stats)

can become :

maxofHistogram stats = foldl' max 0 (map snd stats)

("foldl' max 0" could be replaced by "maximum" but there wouldn't be a
default 0 anymore)

more importantly, you can replace this kind of code :
  vA <- varCreate []
  vB <- varCreate []
  -- ...
  vL <- varCreate []
  vM <- varCreate []
  vN <- varCreate []
  vO <- varCreate []

by :
  [vA, vB, vC, vD, vE, vF, vG, vH, vI, vJ, vK, vL, vM, vN, vO] <-
    replicateM 15 (varCreate [])

(true also for the "dA <- textEntry statusFrame [text := "0",
alignment := AlignRight]" sequence)

I'm not sure that functions like getdTotal couldn't be improved, I
wonder if a small Map for the elements of d wouldn't make the code
much better and offer other opportunities for abstractions. As it is,
enumeration like :

             [[label "Total Entries",   widget (getdTotal d)]
             ,[label "Valid Entries",   widget (getdValid d)]
             -- ...
             ,[label "MDMA",            widget (getdMdma d)]
             ,[label "Caffeine",        widget (getdCaffeine d)]]

could be slightly reduced by :
let bindLabelAndWidget (lbl,getter) = [label lbl, widget (getter d)]
in map bindLabelAndWidget [("Total Entries", getdTotal), ("Valid
Entries", getdValid)
  ,(...)]

And little thing like :
mapM_ (\f -> do repaint f) knownFrames
becoming :
mapM_ repaint knownFrames


I also do concur that a flag or a warning to signal mixed tabulations
and space would be a _very_ good idea !

--
Jedaï
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[Don Stewart-2]

chaddai.fouche:

> 2008/3/4, Alan Carter <alangcarter@...>:
> >  I've written up some reflections on my newbie experience together with
> >  both versions, which might be helpful to people interested in
> >  popularizing Haskell, at:
> >
> >  http://the-programmers-stone.com/2008/03/04/a-first-haskell-experience/
>
>
> I also do concur that a flag or a warning to signal mixed tabulations
> and space would be a _very_ good idea !
>

Such a flag already exists:

    -fwarn-tabs

As in:

    $ ghc -fwarn-tabs A.hs -no-recomp
    A.hs:3:0: Tab character

-- Don
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[Lennart Augustsson]

Thanks for an interesting write-up.  And not bad for a first Haskell program. :)
There's still a number of things you could do to limit the boiler plate code, though.

On Tue, Mar 4, 2008 at 6:29 AM, Alan Carter <alangcarter@...> wrote:

Many thanks for the explanations when I was first experimenting with
Haskell. I managed to finish translating a C++ wxWidgets program into
Haskell wxHaskell, and am certainly impressed.

I've written up some reflections on my newbie experience together with
both versions, which might be helpful to people interested in
popularizing Haskell, at:

http://the-programmers-stone.com/2008/03/04/a-first-haskell-experience/

Regards,

Alan

--
... the PA system was moaning unctuously, like a lady hippopotamus
reading A. E. Housman ..."
 -- James Blish, "They Shall Have Stars"
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[Richard O'Keefe]

Concerning the Haskell program that does some statistics and displays  
some graphs,
I must say that if that were the task I had to solve I would not use  
either C++ or Haskell,
but R, the open source S lookalike.  The best way to be productive as  
a programmer
is to not write code if you can steal it.  R looks like an imperative  
language, but it is
"value-oriented" in the same way that SETL is, so is by some criteria  
a functional language
of sorts.

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