Re: [Babel] Handling of errors when using Ledger

[Eric S Fraga <ucecesf@ucl.ac.uk>]

Dan Davison <dandavison7@gmail.com> writes:

> Eric S Fraga <ucecesf@ucl.ac.uk> writes:
>
>> Dan <dandavison7@gmail.com> writes:
>>
>> [...]
>>
>>> This patch should make ob-ledger use the common org-babel error mechanism. It is
>>> in branch ledger of the main repo. However, I'm not yet a ledger user. Could
>>> someone test it?
>>
>> Unfortunately, it doesn't work at all [1] for a very simple reason: you
>> have removed the -f option which specifies the file that ledger should
>> read.
>
> Hi Eric,
>
> Yes, ob-eval passes the src block body to the interpreter on standard
> input. I assumed that ledger would be able to read its transaction data
> from standard input. Is that not the case?  What about with "--file -"
> or "-f -"?

> [...]

> If ledger can't read the src blocks body from stdin (and if it can't, I
> expect there's a good reason why not), then maybe this is a motivation
> for changing ob-eval so that the block body is read from file.

Indeed, ledger cannot read from standard input.  From the man page:

,----
|  All commands require a Ledger data file which can be specified with -f
|  filename or via the LEDGER_FILE environment variable.
`----

and later:

,----
|  -f, --file FILE
| 
|     Reads FILE as a Ledger file. This option may be specified multiple
|     times.  FILE may also be a list of file names separated by colons.
|     Typically, the environment variable LEDGER_FILE is set rather than
|     using this command-line option.
`----

Using an environment variable is not a good or viable solution for
babel, as far as I can figure, and there does not seem to be any concept
of "-" for standard input in lieu of a file.  I cannot see any reason
for this and, to be honest, I find it annoying [1] as a long time Unix user
wishing to join tools together with pipes etc.  But maybe John Wiegley
had his reasons for taking this decision.  Maybe he can comment on
this... I think he reads this list?

> Incidentally, I have for a long time wondered whether we should permit
> src blocks to read *input data* from standard input. This would require
> altering ob-eval such that the src block body is read from file. Then we
> could do things like
>
> #+source: output-some-text
> #+begin_src sh :results output
>   # print stuff
> #+end_src
> #+begin_src perl :stdin output-some-text
>   while ( <> ) {
>       # process the text
>   }
> #+end_src

This could be a solution.  In thinking about all of my babel uses, this
would have no impact on me but others may have different opinions?  It
would seem to be a safer route in any case?

Thanks,
eric


Footnotes: 
[1]   but not annoying enough to stop using ledger, of course, as it's a
      brilliant tool otherwise!

-- 
: Eric S Fraga (GnuPG: 0xC89193D8FFFCF67D) in Emacs 23.2.1
: using Org-mode version 7.3 (release_7.3.99.g9db0.dirty)