Getting the name of file-like objects

Getting the name of file-like objects

[Justin Veilleux]

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Hi everyone. I'm currently writing a set of helper functions (usually 
written using `computed-file`  which act on file like objects to 
transform them in some way.
For instance, I have a `decompress` function which, given a file-like 
object pointing to an archive, will return a computed file object which 
it will decompress to it's output.
Everything works very well, but I would like to be able to name the 
`computed-file` objects something meaningfull.

```
(define (unzip f)
   (computed-file (string-append (name f) "-unzipped")
     #~(begin
         (system* (string-append #$unzip "/bin/unzip")
                  "-d" #$output
                  #$file))
          #$out))
```

Is there someting which ressembles the imaginary `name` function I used 
above?

Cheers.

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Re: Getting the name of file-like objects

[Maxime Devos]

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Justin Veilleux schreef op vr 01-04-2022 om 16:29 [-0400]:
> (define (unzip f)
>   (computed-file (string-append (name f) "-unzipped")
>     #~(begin
>         (system* (string-append #$unzip "/bin/unzip")

(unrelated) you can do #+(file-append unzip "/bin/unzip") here.  The
'file-append' is not very important here, but the #+ is.  The
difference between #+ (cf. 'native-inputs) and #$ (cf. 'inputs') is
important when cross-compiling.

Also, I would use 'invoke' instead of 'system*' here -- 'invoke' throws
an exception if it fails (making the derivation fail to build), whereas
'system*' silently returns an integer.

>                  "-d" #$output
>                  #$file))
>          #$out))
> ```
> 
>     Is there someting which ressembles the imaginary `name` function
>       I used above?

computed-file-name, local-file-name, package-name ...  I don't think
there's some generic procedure for this.

Greetings,
Maxime.

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Re: Getting the name of file-like objects

[Ludovic Courtès]

Hi,

Maxime Devos <maximedevos@telenet.be> skribis:

> computed-file-name, local-file-name, package-name ...  I don't think
> there's some generic procedure for this.

IWBN to address that and have a generic procedure, somehow.

Ludo’.

Re: Getting the name of file-like objects

[Liliana Marie Prikler]

Hi Justin

Am Freitag, dem 01.04.2022 um 16:29 -0400 schrieb Justin Veilleux:
>  Hi everyone. I'm currently writing a set of helper functions
> (usually written using `computed-file`  which act on file like
> objects to transform them in some way.
> For instance, I have a `decompress` function which, given a file-like
> object pointing to an archive, will return a computed file object
> which it will decompress to it's output.
>  Everything works very well, but I would like to be able to name the
> `computed-file` objects something meaningfull.
> ```
> (define (unzip f)
>   (computed-file (string-append (name f) "-unzipped")
>     #~(begin
>         (system* (string-append #$unzip "/bin/unzip")
>                  "-d" #$output
>                  #$file))
>          #$out))
> ```
> Is there someting which ressembles the imaginary `name` function I
> used above?
Generally speaking, you'll have to speak to the store to achieve your
goal.  For a specific implementation, that fetches a file from a
package (without building the package in question!), see package-file
in (guix packages).

Cheers