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14.10 Noweb reference syntax

The “noweb” (see http://www.cs.tufts.edu/~nr/noweb/) Literate Programming system allows named blocks of code to be referenced by using the familiar Noweb syntax:

     <<code-block-name>>

When a code block is tangled or evaluated, whether or not “noweb” references are expanded depends upon the value of the :noweb header argument. If :noweb yes, then a Noweb reference is expanded before evaluation. If :noweb no, the default, then the reference is not expanded before evaluation. See the noweb-ref header argument for a more flexible way to resolve noweb references.

It is possible to include the results of a code block rather than the body. This is done by appending parenthesis to the code block name which may optionally contain arguments to the code block as shown below.

     <<code-block-name(optional arguments)>>

Note: the default value, :noweb no, was chosen to ensure that correct code is not broken in a language, such as Ruby, where <<arg>> is a syntactically valid construct. If <<arg>> is not syntactically valid in languages that you use, then please consider setting the default value.

Note: if noweb tangling is slow in large Org mode files consider setting the *org-babel-use-quick-and-dirty-noweb-expansion* variable to true. This will result in faster noweb reference resolution at the expense of not correctly resolving inherited values of the :noweb-ref header argument.