As you get more comfortable attaching behavior to tags using tag functions, you'll likely want to create some functions that can be shared between multiple source files. The @filepath{directory-require.rkt} file is a special file that is automatically imported by Pollen source files in the same directory. So every function and value provided by @filepath{directory-require.rkt} can be used in these Pollen files.
As you get more comfortable attaching behavior to tags using tag functions, you'll likely want to create some functions that can be shared between multiple source files. The @filepath{directory-require.rkt} file is a special file that is automatically imported by Pollen source files in the same directory (including within subdirectories). So every function and value provided by @filepath{directory-require.rkt} can be used in these Pollen files.
First, using this file is not mandatory. You can always import functions and values from another file using @racket[require] (as seen in the previous section). The @filepath{directory-require.rkt} is just meant to cure the tedium of importing the same file into every Pollen source file in your project. In a small project, not much tedium; in a large project, more.
Second, notice from the @filepath{.rkt} suffix that @filepath{directory-require.rkt} is a source file containing Racket code, not Pollen code. This is the default because while Pollen is better for text-driven source files, Racket is better for code-driven source files. Still, the choice is yours: the name of this file can be changed by resetting the @racket[world:directory-require] value.
Second, notice from the @filepath{.rkt} suffix that @filepath{directory-require.rkt} is a source file containing Racket code, not Pollen code. This is the default because while Pollen is better for text-driven source files, Racket is better for code-driven source files.
Third, the @filepath{directory-} prefix represents the minimum scope for the file, not the maximum. Pollen source files nested in subdirectories will look for a @filepath{directory-require.rkt} in their own directory first. But if they can't find it, they'll look in the parent directory, then the next parent directory, and so on. Thus, by default, a @filepath{directory-require.rkt} in the root folder of a project will apply to all the source files in the project. But when you add a new @filepath{directory-require.rkt} to a subdirectory, it will apply to all files underneath.
Third, the @filepath{directory-} prefix represents the minimum scope for the file, not the maximum. Pollen source files nested in subdirectories will look for a @filepath{directory-require.rkt} in their own directory first. But if they can't find it, they'll look in the parent directory, then the next parent directory, and so on. Thus, by default, a @filepath{directory-require.rkt} in the root folder of a project will apply to all the source files in the project. But when you add a new @filepath{directory-require.rkt} to a subdirectory, it will apply to all files in that subdirectory and below.
@margin-note{Though a subdirectory-specific @filepath{directory-require.rkt} will supersede the one in the enclosing directory, you can still use @racket[(require "../directory-require.rkt")] to pull in definitions from above, and @racket[provide] to propagate them into the current subdirectory. For instance, @racket[(provide (all-from-out "../directory-require.rkt"))] will re-export everything.}
@margin-note{Though a subdirectory-specific @filepath{directory-require.rkt} will supersede the one in the enclosing directory, you can still use @racket[(require "../directory-require.rkt")] to pull in definitions from above, and @racket[provide] to propagate them into the current subdirectory. For instance, @racket[(provide (all-from-out "../directory-require.rkt"))] will re-export everything from the parent directory.}
Let's see how this works in practice. In the same directory as @filepath{article.html.pm}, create a new @filepath{directory-require.rkt} file as follows:
