Re: [racket-users] Example of file i/o?

[Neil Van Dyke]

Since newbies are always listening, I'll just mention something a lot of 
people here (including Greg) already know. :)


Something like `file->lines` is a handy convenience, when you know the 
file size won't break your system, and/or you're not writing reusable or 
long-lived code.


Good practice for important and reusable code often means doing this 
serial file processing as iteration (or folds) over the input port, and 
processing as you go, rather than sucking an entire file into memory first.


Not all line-based file-processing tasks are serial like this, but I'd 
guess that most are (or, even if you have to do some non-serial 
processing, it can usually be done in a more space-efficient way than 
representing the entire file in memory).


It's good to get comfortable with this.  You don't see it only in simple 
line-oriented file processing, but that's a good playground for 
learning.  Many software frameworks at the moment obscure computational 
time and space factors (and often hide massive loads of crud piled atop 
crud atop crud, especially in in client-side Web frameworks).  But your 
Racket programs are one environment in which you can often still have a 
pretty good idea of what's going on, and grow as a programmer.  If any 
newbies are not convinced, I'll just say "big data" here, as one 
buzzwordy example. :)  When, for example, we suddenly need to invent a 
way to decompose big data processing to use specialized compute 
clusters, that's a job for someone who can understand things, not 
someone who spent all their time only learning how to cargo-cult their 
way through someone else's crappy Web frameworks. :)


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Re: [racket-users] Example of file i/o?

[Leith]

That's exactly what I was trying to do - thanks!

On Wed, Jul 19, 2017 at 12:26 PM, Greg Hendershott <
greghendersh...@gmail.com> wrote:

> If you frequently want to deal with files as a list of lines, you
> could wrap the code Ben showed you in a function:
>
> (define (file->lines file)
>   (with-input-from-file file
> (λ ()
>   (for/list ([line (in-lines)])
> line
>
> As it happens, Racket already defines this function for you:
>
>   https://docs.racket-lang.org/reference/Filesystem.html#%
> 28def._%28%28lib._racket%2Ffile..rkt%29._file-~3elines%29%29
>

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Re: [racket-users] Example of file i/o?

[Greg Hendershott]

If you frequently want to deal with files as a list of lines, you
could wrap the code Ben showed you in a function:

(define (file->lines file)
  (with-input-from-file file
(λ ()
  (for/list ([line (in-lines)])
line

As it happens, Racket already defines this function for you:

  
https://docs.racket-lang.org/reference/Filesystem.html#%28def._%28%28lib._racket%2Ffile..rkt%29._file-~3elines%29%29

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Re: [racket-users] Example of file i/o?

[Leith]

Very good, thank you!

On Tuesday, July 18, 2017 at 11:54:14 AM UTC-5, Ben Greenman wrote:
> (with-input-from-file "file.txt"
>   (lambda ()
>     (for ((line (in-lines)))
>       )))
> 
> 
> On Tue, Jul 18, 2017 at 12:46 PM, Leith  wrote:
> Basic question, but I can't seem to find a good answer.  What is an example 
> of "idiomatic" file I/O using racket?  Like, for example, open a file for 
> reading and do something with every line in the file?
> 
> 
> 
> The example here: https://docs.racket-lang.org/guide/io-patterns.html  says 
> "If you want to process individual lines of a file" but then it doesn't open 
> a file at all.  It uses open-input-string.  I'm guessing it would be 
> sufficient to use open-input-file instead?  Also, what is the right way to 
> read a line at a time until EOF?
> 
> 
> 
> Thanks!
> 
> 
> 
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Re: [racket-users] Example of file i/o?

[Ben Greenman]

(with-input-from-file "file.txt"
  (lambda ()
(for ((line (in-lines)))
  )))

On Tue, Jul 18, 2017 at 12:46 PM, Leith  wrote:

> Basic question, but I can't seem to find a good answer.  What is an
> example of "idiomatic" file I/O using racket?  Like, for example, open a
> file for reading and do something with every line in the file?
>
> The example here: https://docs.racket-lang.org/guide/io-patterns.html
> says "If you want to process individual lines of a file" but then it
> doesn't open a file at all.  It uses open-input-string.  I'm guessing it
> would be sufficient to use open-input-file instead?  Also, what is the
> right way to read a line at a time until EOF?
>
> Thanks!
>
> --
> You received this message because you are subscribed to the Google Groups
> "Racket Users" group.
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>

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[racket-users] Example of file i/o?

[Leith]

Basic question, but I can't seem to find a good answer.  What is an example of 
"idiomatic" file I/O using racket?  Like, for example, open a file for reading 
and do something with every line in the file?

The example here: https://docs.racket-lang.org/guide/io-patterns.html  says "If 
you want to process individual lines of a file" but then it doesn't open a file 
at all.  It uses open-input-string.  I'm guessing it would be sufficient to use 
open-input-file instead?  Also, what is the right way to read a line at a time 
until EOF?

Thanks!

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