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Today's Topics:
1. Re: general observation about programming (Rein Henrichs)
2. Re: Folders and sub-folders (Mike Houghton)
----------------------------------------------------------------------
Message: 1
Date: Fri, 26 Feb 2016 17:41:40 +0000
From: Rein Henrichs <rein.henri...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>,
dbro...@runforyourlife.org
Subject: Re: [Haskell-beginners] general observation about programming
Message-ID:
<cajp6g8yoxf_raw132pzw_9+pxqdp1gmw00dcjfam9ixhrl_...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Pointfree is good for reasoning about *composition*. It can often be more
readable than pointful code when the focus of the function is on
composition of other functions. For example, take this function from
Bird's *Pearls
of Functional Algorithm Design*:
boxes = map ungroup . ungroup . map cols . group . map group
Compare the pointful version:
boxes matrix = map ungroup (ungroup (map cols (group (map group matrix))))
Readibility is subjective, but I think many people will agree that the
pointfree version is easier to read.
On Fri, Feb 26, 2016 at 8:19 AM MJ Williams <matthewjwilliams...@gmail.com>
wrote:
> As I see it, Haskell and pure functional languages aren't
> `necessarily' about readability so much as expressing thought in
> mathematical terms. The readability comes with the consistency and
> transparency of well-formed mathematical notation.
> by the way, that's transparency in laymen's sense and not referential
> transparency.
> Matthew
>
>
> On 26/02/2016, Dudley Brooks <dbro...@runforyourlife.org> wrote:
> > One problem is that, while the symbolic operators do seem to have names
> > (specified in the standards?) which are often sufficiently explanatory,
> > you can find many tutorials which never even mention those names.
> >
> > On 2/26/16 1:55 AM, Mike Pentney wrote:
> >
> >> As a newbie, something I dislike about Haskell is the use of infix
> >> operators like <||> which are unpronouncable and therefore (if you
> >> don't happen to know the notation the symbol is based on) are more or
> >> less meaningless.
> >>
> >> And Haskellers often seem to prefer 1 and 2 character variable names,
> >> which again convey little or no information.
> >>
> >> And don't get me started on point-free code...!
> >>
> >> N.B. I am not trying to start a flame war, these are just comments
> >> from my experience of trying to get beyond text-book examples and
> >> start using Haskell libraries and trying to learn from open source
> >> code. In general I find idiomatic Haskell hard to understand, and for
> >> me this is a barrier to using Haskell for real projects. Maybe someday
> >> I'll have learnt enough to get past this problem, but as the language
> >> and libraries seem to evolve quickly, I have my doubts...
> >>
> >>
> >> On 25/02/16 19:19, Jeffrey Brown wrote:
> >>> Something I like about functional programming is how it interfaces
> >>> with natural language.
> >>> Haskell, somehow to a greater extent than other languages, encourages
> >>> me to divide functions
> >>> into one or two-liners. Each has a type signature that means
> >>> something in English. Further, each
> >>> gives you the opportunity to choose a good name for the function and
> >>> its arguments. After doing
> >>> those things, the function is much easier to write, and much easier
> >>> to read -- so much so that
> >>> often you don't have to read the function body at all, just the type
> >>> signature, function name
> >>> and argument names.
> >>>
> >>> On Thu, Feb 25, 2016 at 8:17 AM, Dudley Brooks
> >>> <dbro...@runforyourlife.org
> >>> <mailto:dbro...@runforyourlife.org>> wrote:
> >>>
> >>> Ages and ages ago I saw this advice about programming:
> >>>
> >>> Q: "What's the best language for a programmer to know?"
> >>>
> >>> A: "English" (or whatever your native language is)
> >>>
> >>> -- Dudley
> >>>
> >>>
> >>> On 2/24/16 4:03 PM, Dennis Raddle wrote:
> >>>
> >>>> This is more about programming in general than Haskell, although
> >>>> Haskellers probably know
> >>>> it well.
> >>>>
> >>>> I don't claim to have expert knowledge on this, but I'm
> >>>> gradually getting better at it.
> >>>>
> >>>> When I set out to write a program, or refactor a program, or
> >>>> modify a program, it helps to
> >>>> set out my thinking in a clear way. And how I make it clear is
> >>>> to document my thoughts.
> >>>>
> >>>> An outline is one good way to organize thoughts and is probably
> >>>> my main tool. But good
> >>>> English prose is also helpful.
> >>>>
> >>>> The key factor is "editing." In what sense do I mean that? Good
> >>>> writers do it, and the
> >>>> Haskell documentation does it. I mean (1) brevity and (2) good
> >>>> flow. To achieve brevity,
> >>>> you must think about the essence of each statement and trim away
> >>>> the unnecessary stuff.
> >>>> Good flow refers to how the document builds up and modifies your
> >>>> concepts as you read it.
> >>>> A document can actually mirror an effective learning process, or
> >>>> influence and change your
> >>>> process.
> >>>>
> >>>> I work with my documentation, making several editing passes. By
> >>>> the time I'm done, I am in
> >>>> a great position to write a concise and flexible program.
> >>>>
> >>>> It's interesting that not only is Haskell a concise language,
> >>>> but the Haskell library
> >>>> documentation is concise. Contrast that with the Python
> >>>> documentation which often wanders
> >>>> about into areas that are irrelevant--it could easily be cut
> >>>> into one third its present size.
> >>>>
> >>>> Mike
> >>>>
> >>>>
> >>>>
> >>>>
> >>>> _______________________________________________
> >>>> Beginners mailing list
> >>>> Beginners@haskell.org <mailto:Beginners@haskell.org>
> >>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
> >>>
> >>>
> >>> _______________________________________________
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> >>>
> >>>
> >>>
> >>>
> >>> --
> >>> Jeffrey Benjamin Brown
> >>>
> >>>
> >>> _______________________________________________
> >>> Beginners mailing list
> >>> Beginners@haskell.org
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> >>>
> >> _______________________________________________
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Message: 2
Date: Fri, 26 Feb 2016 18:13:33 +0000
From: Mike Houghton <mike_k_hough...@yahoo.co.uk>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Folders and sub-folders
Message-ID: <6d1f3b6c-a168-4c94-bc17-1e1240b31...@yahoo.co.uk>
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Cool, thanks.
> On 26 Feb 2016, at 13:01, Sylvain Henry <hsy...@gmail.com> wrote:
>
> Your "isOk" function will filter out hidden directories on Unix (which may be
> what you want?).
>
> Otherwise: isOk = (`notElem` [".",".."])
>
> Also "\x -> folders x" = "folders"
>
> 2016-02-26 11:42 GMT+01:00 Mike Houghton <mike_k_hough...@yahoo.co.uk
> <mailto:mike_k_hough...@yahoo.co.uk>>:
> Thanks.
>
>
> I sweated it bit more and got
>
>
>
> isOk FilePath -> Bool
> isOk = not . isPrefixOf "."
>
> folders :: FilePath -> IO [FilePath]
> folders fp = do
> all <- getDirectoryContents fp
> z' <- filterM doesDirectoryExist $ map (fp </>) (filter isOk all)
> x' <- mapM (\x -> folders x) z'
> return $ z' ++ (concat x') ::
>
> which seems to work.
>
>
> > On 25 Feb 2016, at 19:07, Imants Cekusins <ima...@gmail.com
> > <mailto:ima...@gmail.com>> wrote:
> >
> > Hello Mike,
> >
> > below code find all files recursively from a starting point. It works.
> >
> > You'd need to tweak it to find folders instead.
> >
> >
> > import System.Directory
> > import Data.List
> >
> >
> > findAllFiles::FilePath -> IO [FilePath]
> > findAllFiles base0 = gd1 base0
> >>> = \list1 -> concatMap' recurse3 list1
> > where gd1 d1 = filter f2 <$> (getDirectoryContents d1)
> > f2 "." = False
> > f2 ".." = False
> > f2 _ = True
> > recurse3 md3 = doesDirectoryExist md3full
> >>> = \isDir3 ->
> > if isDir3 then findAllFiles md3full
> > else pure [md3full]
> > where md3full = base0 ++ "/" ++ md3
> >
> >
> >
> > concatMap':: (a -> IO [b]) -> [a] -> IO [b]
> > concatMap' m0 list0 = sequence (m0 <$> list0)
> >>> = \list2 -> pure $ concat list2
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