How to pass newline ("\n") string to noweb <<call>>

I understand your confusion.

The good news is that your code is already passing new lines correctly into your noweb call.

The reason you're seeing the eval: Symbol’s value as variable is void: a error is because of the generated elisp code.

If you execute the following code you'll see the same error message:

#+BEGIN_src elisp a b c #+END_src 

A convenient way to preview how code will be rendered by noweb is to put cursor inside you block and press C-c C-v v.

Another way to preview code is to render the code in multiple steps:

#+NAME: sql-stmt #+BEGIN_SRC sql :noweb yes :eval never insert into table select @SPID, <<pr("1\n2\n3\n4")>> #+END_SRC #+BEGIN_SRC css :noweb yes :wrap "src sql" <<sql-stmt>> #+END_SRC #+RESULTS: #+BEGIN_src sql insert into table select @SPID, 1 select @SPID, 2 select @SPID, 3 select @SPID, 4 #+END_src 

Note You should be cautious when generating SQL statements this way because it is very easy to accidentally introduce a SQL injection vulnerability into your source code. Be sure to verify your data and sql statements before executing against your database.

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This code was tested using:
GNU Emacs 25.3.1 (x86_64-apple-darwin16.7.0, NS appkit-1504.83 Version 10.12.6 (Build 16G29))
org-mode version: 9.1.2