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Today's Topics:
1. Re: Where to report an unfriendly feature (if not a bug) in
`stack ghci`? (Jeffrey Brown)
2. Re: Storing the time difference between two Monotonic time
results (David McBride)
3. Haskell for Imperative Programmers (Olivier Revollat)
----------------------------------------------------------------------
Message: 1
Date: Mon, 9 Jul 2018 14:29:46 -0500
From: Jeffrey Brown <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Where to report an unfriendly feature
(if not a bug) in `stack ghci`?
Message-ID:
<caec4ma3eqyixnt9-rldzfu0tzxaf-rxi-_5wq6hudxrahua...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Strange -- that page indicates the suggestion was applied, but when I try
it, it doesn't work:
Configuring GHCi with the following packages:
GHCi, version 8.2.2: http://www.haskell.org/ghc/ :? for help
Loaded GHCi configuration from /tmp/ghci10227/ghci-script
Prelude> :set prompt "> "
> :{
Prelude| 3
Prelude| :}
3
> :set prompt2 "> "
Some flags have not been recognized: prompt2, >
> :{
Prelude| 3
Prelude| :}
3
>
On Wed, Jul 4, 2018 at 7:31 AM Ut Primum <[email protected]> wrote:
> Hi,
> I think the same was reported here:
>
> https://ghc.haskell.org/trac/ghc/ticket/7509#no1
>
> Ut
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
--
Jeff Brown | Jeffrey Benjamin Brown
Website <https://msu.edu/~brown202/> | Facebook
<https://www.facebook.com/mejeff.younotjeff> | LinkedIn
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Message: 2
Date: Mon, 9 Jul 2018 15:52:00 -0400
From: David McBride <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Storing the time difference between
two Monotonic time results
Message-ID:
<CAN+Tr43Dt1Bi+Ds=tpydfgj-6hun5+k8pyg6raw3mabx+4d...@mail.gmail.com>
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toList :: String -> [Integer]
toList input = read ("[" ++ input ++ "]")
That was creative, but a more idiomatic way to write that would be to use
the split package
stack ghci --package split
import Data.Split
toList :: String -> [Integer]
toList = fmap read . splitOn ","
As for how to aggregate times, start thinking about the types before you
start. Each iteration you should take a List and return a TimeSpec.
testcase :: [Integer] -> IO TimeSpec
testcase l = do
start <- getTime Monotonic
evaluate (mergesort l)
end <- getTime Monotonic
return $ diffTimeSpec start end
Now, we need to run it 100 times and collect the times. Sounds like a job
for map, but since testcase is monadic, use mapM instead (or traverse).
main = do
unsortedList <- undefined
times <- mapM (\c -> testcase unsortedList) [1..100]
print times
On Mon, Jul 9, 2018 at 9:40 AM, Awsaf Rahman <[email protected]>
wrote:
> Okay, here is what I am trying to do. I am trying to time this mergesort
> program. I want to run this program 100, 1000, etc times and store the
> timing results in a list if possible. Can't seem to figure out how to do
> it! The following program prints the timings to the shell and I need to
> figure out a way to store the timings in a list.
>
>
> {-# LANGUAGE OverloadedStrings #-}
> {-# LANGUAGE BangPatterns #-}
> import Control.Exception
> import Formatting
> import Formatting.Clock
> import System.Clock
> import Control.DeepSeq
>
> mergesort [] = []
> mergesort [x] = [x]
> mergesort xs = let (lhalf, rhalf) = splitAt (length xs `div` 2) xs
> in merge' (mergesort lhalf) (mergesort rhalf)
>
> merge' lhalf rhalf = merge lhalf rhalf []
>
> merge [] [] acc = reverse acc
> merge [] y acc = reverse acc ++ y
> merge x [] acc = reverse acc ++ x
>
> merge (l:ls) (r:rs) acc
> | l < r = merge ls (r:rs) (l:acc)
> | otherwise = merge rs (l:ls) (r:acc)
>
> toList :: String -> [Integer]
> toList input = read ("[" ++ input ++ "]")
>
> repeater unsortedlist 0 result = return (result)
>
> repeater unsortedlist counter result = do
> start <- getTime Monotonic
> evaluate(mergesort unsortedlist)
> end <- getTime Monotonic
> fprint (timeSpecs % "\n") start end
> repeater unsortedlist (counter-1) result
>
> main = do
> file <- getLine
> contents <- readFile file
> let !unsortedlist = (toList contents)
> repeater unsortedlist 100 []
>
>
> On Mon, Jul 9, 2018 at 3:21 PM, David McBride <[email protected]> wrote:
>
>> I guess whatever version you are using did not export that function. In
>> any case the definition for that function is incredibly simple, so you
>> could just write your own for now.
>>
>> diffTimeSpec :: TimeSpec -> TimeSpec -> TimeSpecdiffTimeSpec ts1 ts2 = abs
>> (ts1 - ts2)
>>
>>
>>
>> On Mon, Jul 9, 2018 at 9:08 AM, Awsaf Rahman <[email protected]>
>> wrote:
>>
>>> I imported the System.Clock module and tried to use the diffTimeSpec
>>> function but it keeps saying "out of scope".
>>>
>>> On Mon, Jul 9, 2018 at 2:45 PM, David McBride <[email protected]> wrote:
>>>
>>>> There is a diffTimeSpec function in that module that seems like it
>>>> would work.
>>>>
>>>> On Mon, Jul 9, 2018 at 8:30 AM, Awsaf Rahman <[email protected]
>>>> > wrote:
>>>>
>>>>> Hello,
>>>>>
>>>>> I am trying to time a function I have written in haskell using the
>>>>> clock package in the following way:
>>>>>
>>>>> *start <- getTime Monotonic*
>>>>> *evaluate(something)*
>>>>> *end <- getTime Monotonic*
>>>>> *fprint (timeSpecs % "\n") start end*
>>>>>
>>>>>
>>>>> Now what I want is to store the time difference between *start* and *end.
>>>>> *Is there a way I can do that?
>>>>>
>>>>> Regards
>>>>> Awsaf
>>>>>
>>>>> _______________________________________________
>>>>> Beginners mailing list
>>>>> [email protected]
>>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>>>>
>>>>>
>>>>
>>>> _______________________________________________
>>>> Beginners mailing list
>>>> [email protected]
>>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>>>
>>>>
>>>
>>> _______________________________________________
>>> Beginners mailing list
>>> [email protected]
>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>>
>>>
>>
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>>
>
> _______________________________________________
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>
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Message: 3
Date: Tue, 10 Jul 2018 11:22:17 +0200
From: Olivier Revollat <[email protected]>
To: [email protected]
Subject: [Haskell-beginners] Haskell for Imperative Programmers
Message-ID:
<ca+nxgrwb0p7rjw0ggbfotql+_-ogpmxcr9cwfepebax9uei...@mail.gmail.com>
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Hi,
I've been using imperative languages for 20 years now :)
I'm a beginner in haskell and I love the paradigm shift you feel when you
come from imperative programming. I found interesting articles like :
https://wiki.haskell.org/Haskell_IO_for_Imperative_Programmers
Do you have any other ressources like that ?
I'm not looking for how to use haskell in imperative style (e.g. with "do"
notation, ...) no no ! I'm looking articles who explain how NOT TO USE
imperative style with haskell, and help thinking the paradigm shift ...
Thanks :)
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