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Today's Topics:
1. Re: Parsing (Mike Houghton)
2. Re: haskell + python numpy (Daniel Bergey)
3. better way: contains one of a string from list in a string
(Miro Karpis)
4. Re: better way: contains one of a string from list in a
string (Lyndon Maydwell)
5. How to call popCnt64#? (John Ky)
----------------------------------------------------------------------
Message: 1
Date: Sat, 19 Mar 2016 13:19:36 +0000
From: Mike Houghton <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Parsing
Message-ID: <[email protected]>
Content-Type: text/plain; charset=utf-8
Hi,
Just to recap I wanted to parse name:value pairs where some pairs are mandatory
and some are not.
eg
//these are mandatory
location : /user/local
target : /x/y
//these are optional
copyTo : /a/b
trace : bla blah ,,,
undo : etc etc
so I made
data Item = Item (Name, Value) deriving (Show)
where Name, Value are strings and made a parser for it.
-- KeyWordItemParser
kwip :: String -> Parser Item
kwip keyWord = do
spaces
name <- string keyWord
spaces
char ':'
spaces
val <- itemValue
spaces
return $ Item (name, val)
I made the mandatory of fixed order and hence easy to parse.
For the optional I ended up defining a fixed order in which they can appear
if indeed they do appear.
So, for example, ?copyTo' has to come before ?trace?
This allowed code like
many $ kwip ?copyTo"
many $ kwip ?trace"
many $ kwip ?undo"
which of course may result in duplicates that are later flagged as errors in
post parsing validation. This validation step was needed
anyway for other checking so a bit more was sort of ok.
Pragmatically speaking It works ok but I?m not really happy with it. I?d really
like to not have to enforce order.
What I have been considering but have not yet been able to articulate in
Haskell is, for parsing the optionals in any order, is to create a list of
parsers and apply whilst removing parsers from the list. i.e. in pseudo code?
Try to parse
A : w
B : x
C : y
D : z
in any order
parserList = [kwip A, kwip B, kwip C, kwip D]
parse list text = do
parserList empty? then done
try a parser from parserList until one works - if none work then done (or
error)
if one worked accumulate result
remove succesful parser from parserList then call again
Any advice on how to write this in Haskell would be appreciated.
Many thanks
Mike
> On 6 Mar 2016, at 10:17, Francesco Ariis <[email protected]> wrote:
>
> On Sun, Mar 06, 2016 at 09:54:34AM +0000, Mike Houghton wrote:
>> Hi Francesco,
>> Quick response! Thanks.
>>
>> I see, so would it reduce to something like?
>> many itemValue
>>
>> and originally I was thinking the data structure that it would parse
>> into would be
>>
>> data Module = Module {? some record structure?}
>>
>> but now it would be roughly like?
>>
>> type Entry = (String, String)
>>
>> data Module = Module [Entry]
>>
>> Thanks
>
> Yes, it would lead to some kind of (YourType, String) association list.
> If you are more interested in a datatype with records I see two
> ways of achieving it:
>
> a. a function `[(YrType, String)] -> RecordsData` (not so
> pretty but doable, also you can check for well-formedness here)
> (Using a sum type YrType is in my opinion better than plain
> Strings as it catches some more errors at compile time).
>
> b. directly via parsing, using `optionMaybe` and glue.
> Depending on how your input is structured this may or may not be
> more hairy (can name and source appear after an optional tag?
> What about duplicated tags? etc.).
> In its simplest form you can use a succinct applicative-style,
> but the castle crumbles if want more.
>
>
> See which fits better (I suspect a.), play with it and report
> back; parsing has never been an elegant business!
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
Message: 2
Date: Sat, 19 Mar 2016 09:58:32 -0400
From: Daniel Bergey <[email protected]>
To: PICCA Frederic-Emmanuel
<[email protected]>,
"beginners\@haskell.org" <[email protected]>
Subject: Re: [Haskell-beginners] haskell + python numpy
Message-ID:
<874mc2lgc7.fsf@chladni.i-did-not-set--mail-host-address--so-tickle-me>
Content-Type: text/plain
I've seen a couple of blog posts (with code) about calling Python from
Haskell. I haven't tried any of this code myself, and I can't recall
seeing anything specifically about Numpy types.
circa 2010: https://john-millikin.com/articles/ride-the-snake/
2014:
http://www.lunaryorn.com/2014/04/15/calling-python-from-haskell.html
2014-2015: https://github.com/Russell91/pyfi
bergey
On 2016-03-19 at 07:47, PICCA Frederic-Emmanuel
<[email protected]> wrote:
> Hello,
>
> I would like to use some python code in order to do my computation with
> haskell.
> The idea is to use python and all it's numrical stack in some places, until I
> find the time to replace the python code by some haskell code.
>
> what I will do is
>
> read the data from hdf5 with bindings-hdf5 in haskell
> obtain a Storable for all my data images
> then I would like to create a python object which will use these data in
> order to generate in return another array.
>
> get back this array and put it into another hdf5 file.
>
> Indeed I want to do this with the pipes library.
>
> I would like to know if someone have some code examples for this kind of use
> case.
>
> interfacing haskell with python numpy object back and forth.
>
> thanks for your help
>
> Frederic
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
------------------------------
Message: 3
Date: Sun, 20 Mar 2016 08:02:07 +0100
From: Miro Karpis <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] better way: contains one of a string from
list in a string
Message-ID:
<CAJnnbxG0ZM3KFW7no=q7dcbepp7wonqxjfj+v_pck_f__mu...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
I needed a function that returns True/False if a list of strings are in a
given string. I made one function below (works fine),..but I was wondering
whether there is a shorter way?
-- |Returns True if one of given strings are contained in given string
contains :: [String] -> String -> Bool
contains elements seach_elem
| trueListCount == 0 = False
| otherwise = True
where
isInStringList = [isInfixOf elem seach_elem | elem <- elements]
onlyTrueList = [elem | elem <- isInStringList, elem == True]
trueListCount = length onlyTrueList
Cheers,
-m
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Message: 4
Date: Sun, 20 Mar 2016 18:11:24 +1100
From: Lyndon Maydwell <[email protected]>
To: [email protected], The Haskell-Beginners Mailing List -
Discussion of primarily beginner-level topics related to Haskell
<[email protected]>
Subject: Re: [Haskell-beginners] better way: contains one of a string
from list in a string
Message-ID:
<CAM5QZtwtT+ifJ68L3DkWZUdyXeCGtw-3kcs=skpj8nbtvwj...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
You can get that one quite easily using 'any'.
E.g.
[Prelude Data.List] ? let contains xs x = any (`isInfixOf` x) xs
contains :: (Eq a, Foldable t) => t [a] -> [a] -> Bool
[Prelude Data.List] ? contains (words "a b c d efg") "refgood"
True
it :: Bool
[Prelude Data.List] ? contains (words "a b c d efg") "ref"
False
it :: Bool
On Sun, Mar 20, 2016 at 6:02 PM, Miro Karpis <[email protected]>
wrote:
> Hi,
>
> I needed a function that returns True/False if a list of strings are in a
> given string. I made one function below (works fine),..but I was wondering
> whether there is a shorter way?
>
>
> -- |Returns True if one of given strings are contained in given string
> contains :: [String] -> String -> Bool
> contains elements seach_elem
> | trueListCount == 0 = False
> | otherwise = True
> where
> isInStringList = [isInfixOf elem seach_elem | elem <- elements]
> onlyTrueList = [elem | elem <- isInStringList, elem == True]
> trueListCount = length onlyTrueList
>
>
> Cheers,
> -m
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
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------------------------------
Message: 5
Date: Sun, 20 Mar 2016 10:19:50 +0000
From: John Ky <[email protected]>
To: "[email protected]" <[email protected]>
Subject: [Haskell-beginners] How to call popCnt64#?
Message-ID:
<CAMB4o-Cxs0vWdR2a3i-yALVSfU=njvcfz9k9tublanzod4v...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hello Haskellers,
Does anyone know how to call popCnt64# from the GHC.Prim module?
This was my failed attempt:
?> popCnt64# 1
<interactive>:14:11:
Couldn't match kind ?*? with ?#?
When matching types
a0 :: *
Word# :: #
Expected type: Integer -> Word#
Actual type: Integer -> a0
In the first argument of ?popCnt64#?, namely ?1?
In the expression: popCnt64# 1
In an equation for ?it?: it = popCnt64# 1
-John
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