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Today's Topics:
1. Re: Beginners Digest, Vol 100, Issue 20 (Mahdi Dibaiee)
2. Re: Beginners Digest, Vol 100, Issue 20 (Imants Cekusins)
3. Re: Beginners Digest, Vol 100, Issue 19 (Ashish Negi)
4. Re: Beginners Digest, Vol 100, Issue 19 (Norbert Melzer)
5. Re: Beginners Digest, Vol 100, Issue 19 (Matt Williams)
----------------------------------------------------------------------
Message: 1
Date: Sat, 29 Oct 2016 13:18:11 -0400
From: Mahdi Dibaiee <mdiba...@aol.com>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] Beginners Digest, Vol 100, Issue 20
Message-ID: <1581172e335-25c9-3...@webstg-a07.mail.aol.com>
Content-Type: text/plain; charset="utf-8"
That's not generally true (but I will give my guess about your assumption
after this). See the example in the article I linked:
```
import Data.Char(toUpper)
main = do
inpStr <- readFile "input.txt"
writeFile "output.txt" (map toUpper inpStr)
```
Here, `inputStr` has to be evaluated in order to run `map toUpper` on it,
but it's done character by character. Character is read, `toUpper` is run on
it, it's written to the file.
(Though it might not be a character unless we use `NoBuffering`, it's going to
be lines or blocks)
Now, I guess your assumption _might_ be true in my case, because `show` might
not be able to
generate the string character by character (which is very likely), in this
case, show will give us the whole string in one
piece, leading to an out-of-memory error as the big string is getting loaded to
memory in order to be used by `writeFile`.
This is just a guess, I would appreciate it if someone could actually prove it.
What do you think Imants?
-----Original Message-----
From: beginners-request <beginners-requ...@haskell.org>
To: beginners <beginners@haskell.org>
Sent: Sat, Oct 29, 2016 3:44 pm
Subject: Beginners Digest, Vol 100, Issue 20
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Contents of Beginners digest..."Today's Topics: 1. Writing huge result of
`show` to file results in out of memory (Mahdi Dibaiee) 2. Re: Writing huge
result of `show` to file results in out of memory (Imants Cekusins)
Attached Message
From
Mahdi Dibaiee <mdiba...@aol.com>
To
beginners@haskell.org
Subject
[Haskell-beginners] Writing huge result of `show` to file resultsin out of
memory
Date
Fri, 28 Oct 2016 12:57:22 -0400
I know that there are other ways of doing it, I just want to understand
where lies the problem here.
I just read the realworldhaskell book by O'Reilly, in one section, Lazy I/O
[0], it's explained
that there should be no problem writing big strings, without consuming the
whole string
to files, however big they are.
I would appreciate it if someone could point out the problem there.
Thanks
[0]: http://book.realworldhaskell.org/read/io.html#io.lazy
Attached Message
From
Imants Cekusins <ima...@gmail.com>
To
The Haskell-Beginners Mailing List - Discussion of primarily beginner-level
topics related to Haskell <beginners@haskell.org>
Subject
Re: [Haskell-beginners] Writing huge result of `show` to fileresults in out of
memory
Date
Fri, 28 Oct 2016 19:13:23 +0200
> there should be no problem writing big strings, without consuming the whole
> string
lazy means evaluated when needed. However when a string is evaluated, it is
evaluated fully, I guess.
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Message: 2
Date: Sat, 29 Oct 2016 19:46:00 +0200
From: Imants Cekusins <ima...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Beginners Digest, Vol 100, Issue 20
Message-ID:
<cap1qinbh2xof0xo0f-6dfjzz9fsatdtkr_ilwmhhpc+ycj8...@mail.gmail.com>
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here is a very comprehensive explanation of lazy evaluation:
https://github.com/takenobu-hs/lazy_evaluation
I understand < 5% of this so can't add to it.
about your particular problem, I would not try to rely on lazy evaluation
(regardless of how it actually works) but instead break data in chunks,
serialize and write the chunks to disk using libraries. This should work.
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Message: 3
Date: Sun, 30 Oct 2016 14:30:27 +0530
From: Ashish Negi <thisismyidash...@gmail.com>
To: beginners@haskell.org
Subject: Re: [Haskell-beginners] Beginners Digest, Vol 100, Issue 19
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<CAMo8VbFKmDesB4ZOYtoiHE0B3NEdCOfFzb4z9F=fnaafspc...@mail.gmail.com>
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Can you write your own custom function for converting the data structure to
string ?
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Message: 4
Date: Sun, 30 Oct 2016 09:09:43 +0000
From: Norbert Melzer <timmel...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Beginners Digest, Vol 100, Issue 19
Message-ID:
<CA+bCVssuu5U-cw0sfQCR-O=nd89cpodzywphng3xx29fjfv...@mail.gmail.com>
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When replying to the digest, could you provide more context?
Ashish Negi <thisismyidash...@gmail.com> schrieb am So., 30. Okt. 2016
10:00:
> Can you write your own custom function for converting the data structure
> to string ?
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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Message: 5
Date: Sun, 30 Oct 2016 09:18:59 +0000
From: Matt Williams <matt.williams45...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] Beginners Digest, Vol 100, Issue 19
Message-ID:
<caftvgqz6hwudv6m0ovyp4wld_uzr5-bmnmqjlat6wihznoq...@mail.gmail.com>
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I suspect you want to provide your own definition of Show.
Most tutorials show how to do this.
M
On Sun, 30 Oct 2016, 09:00 Ashish Negi, <thisismyidash...@gmail.com> wrote:
> Can you write your own custom function for converting the data structure
> to string ?
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
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