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* [babel] Noweb expansion, not noweb evaluation...
@ 2011-10-31 16:22 Sebastien Vauban
  0 siblings, 0 replies; only message in thread
From: Sebastien Vauban @ 2011-10-31 16:22 UTC (permalink / raw)
  To: emacs-orgmode-mXXj517/zsQ

Hi Eric,

* Overview

In order to be able to create a big code from small chunks, I need to compose
with the *expanded* view of a block, instead of its *evaluated* result.

I don't see how to do that while keeping the small block *executable*.

* Use case

A use case could explain the need in a much clearer manner.

I have a SQL block that duplicates a row:

#+srcname: insert-duplicate-row-with-ID
#+begin_src sql :var table="order" :var column="ID" :var source_value="'73-0007'" :var target_value="'73-0008'"

This block is executable, that is I can call it on the fly to make what I
mean. This is good.

Now, I wanna make use of that general "function" in a long stored procedure,
customized to duplicate a row in a large set of tables. Something like this:

#+begin_src sql :noweb yes
CREATE PROCEDURE clone_row_with_ID
    @source_value varchar(16),
    @target_value varchar(16)
    <<insert-duplicate-row-with-ID("table1", "column", "@source_value", "@target_value")>>
    <<insert-duplicate-row-with-ID("table2", "column", "@source_value", "@target_value")>>
    <<insert-duplicate-row-with-ID("tableN", "column", "@source_value", "@target_value")>>

But this does not work, as Babel replaces the Noweb call with the results of
its evaluation, not with the results of its *expansion*.

Is there a way to get it working?

* Workaround

A very ugly workaround which I see is that:

- the reference block prints out SQL code: for example, an AWK code printing
  SQL statement.

- the general block calls Noweb, and receives the output of AWK's execution,
  hence expanded SQL code.

But, then, the reference block is not executable anymore. Not really a
workaround, then...

Best regards,

Sebastien Vauban

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