These dialects can be invoked one of two ways: either by invoking a specific dialect in the first line of the file (also known as the @tt{#lang} line), or by using the generic @tt{#langpollen} as the first line, and then the correct dialect will be automatically selected based on the source file extension.
@bold{How is this different from Racket?} In Racket, if you try to treat an identifier as a function before defining it with @racket[define], you'll get an error.
The second export, @racket[metas], is a hashtable of key–value pairs with extra information that is extracted from the source. These @racket[metas] will always contain the key @racket['here-path], which returns a string representation of the full path to the source file. Beyond that, the only @racket[metas] are the ones that are specified within the source file (see the source formats below for more detail on how to specify metas).
Pollen source files also make the @racket[metas] hashtable available through a submodule, also called @racket[metas]. So rather than importing a source file with @racket[(require "source.html.pm")], you would @racket[(require (submod "source.html.pm" metas))]. Accessing the metas this way avoids fully compiling the source file, and thus will usually be faster.
The names @racket[doc] and @racket[metas] can be changed for a project by overriding @racket[world:main-export] and @racket[world:meta-export].
@margin-note{The Pollen rendering system relies on these two identifiers, but otherwise doesn't care how they're generated. Meaning, the code inside your Pollen source file could be @tt{#langracket} or @tt{#langwhatever}. As long as you manually @racket[provide] those two identifiers and follow the usual file-naming convention, your source file will be usable.}
@bold{How is this different from Racket?} In Racket, you must explicitly @racket[define] and then @racket[provide] any values you want to export.
@subsection{Custom exports}
Any value or function that is defined within the source file using @racket[define] is automatically exported.
@bold{How is this different from Racket?} In Racket, you must explicitly @racket[provide] any values you want to export. Unlike Racket, every Pollen source file impliedly uses @racket[(provide (all-defined-out))].
If a file called @filepath{pollen.rkt} exists in the same directory with a source file, or in a parent directory of that source file, it's automatically imported when the source file is compiled.
Invoke the preprocessor dialect by using @code{#lang pollen/pre} as the first line of your source file, or by using @code{#lang pollen} with a file extension of @code{@(format ".~a" world:preproc-source-ext)}. These forms are equivalent:
When no dialect is explicitly specified by either the @tt{#lang} line or the file extension, Pollen will default to using the preprocessor dialect. For instance, this file will be treated as preprocessor source:
Invoke the Markdown dialect by using @code{#lang pollen/markdown} as the first line of your source file, or by using @code{#lang pollen} with a file extension of @code{@(format ".~a" world:markdown-source-ext)}. These forms are equivalent:
Invoke the Pollen markup dialect by using @code{#lang pollen/markup} as the first line of your source file, or by using @code{#lang pollen} with a file extension of @code{@(format ".~a" world:markup-source-ext)}. These forms are equivalent:
Invoke the pagetree dialect by using @code{#lang pollen/ptree} as the first line of your source file, or by using @code{#lang pollen} with a file extension of @code{@(format ".~a" world:pagetree-source-ext)}. These forms are equivalent:
The output of the pagetree dialect, provided by @racket[doc], is a @racket[pagetree?] that is checked for correctness using @racket[validate-pagetree].
These aren't source formats because they don't contain a @tt{#lang pollen} line. But for convenience, they get special handling by the Pollen project server.
Files with the null extension are simply rendered as a copy of the file without the extension, so @filepath{index.html.p} becomes @filepath{index.html}.
This can be useful you're managing your project with git. Most likely you'll want to ignore @filepath{*.html} and other file types that are frequently regenerated by the project server. But if you have isolated static files —for instance, a @filepath{index.html} that doesn't have source associated with it —they'll be ignored too. You can cure this problem by appending the null extension to these static files, so they'll be tracked in your source system without actually being source files.
@section{Escaping output-file extensions within source-file names}
Pollen relies extensively on the convention of naming source files by adding a source extension to an output-file name. So the Pollen markup source for @filepath{index.html} would be @filepath{index.html.pm}.
This convention occasionally flummoxes other programs that assume a file can only have one extension. If you run into such a situation, you can @italic{escape} the output-file extension using the @racket[world:extension-escape-char], which defaults to the underscore @litchar{_}.
So instead of @filepath{index.html.pm}, your source-file name would be @filepath{index_html.pm}. When this source file is rendered, it will automatically be converted into @filepath{index.html} (meaning, the escaped extension will be converted into a normal file extension).
This alternative-naming scheme is automatically enabled in every project. You can also set the escape character on a per-project basis (see @racket[world:current-extension-escape-char]). Pollen will let you choose any character, but of course it would be unwise to pick one with special meaning in your filesystem (for instance, @litchar{/}).
