6.1 Scribble Layers

► |  | Scribble: The Racket Documentation Tool

1 | Getting Started
2 | @ Syntax
3 | High-Level Scribble API
4 | Scribbling Documentation
5 | Literate Programming
6 | Low-Level Scribble API
7 | Running scribble
| Index

▼ | 6 | Low-Level Scribble API

6.1 | Scribble Layers
6.2 | @ Reader Internals
6.3 | Structures And Processing
6.4 | Renderers
6.5 | Decoding Text
6.6 | Document Language
6.7 | Document Reader
6.8 | Cross-Reference Utilities
6.9 | Tag Utilities
6.10 | Blue Boxes Utilities
6.11 | Extending and Configuring Scribble Output

► | 6.1 | Scribble Layers

6.1.1 | Typical Composition
6.1.2 | Layer Roadmap

On this page:

6.1.1 Typical Composition
6.1.2 Layer Roadmap

Racket
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### 6.1 Scribble Layers🔗ℹ

Scribble is made of independently usable parts. For example, the Scribble reader can be used in any situation that requires lots of free-form text. You can also skip Scribble’s special reader support, and instead use the document-generation structure directly.

#### 6.1.1 Typical Composition🔗ℹ

A Scribble document normally starts

> #lang scribble/manual

but it could also start

> #lang scribble/base

or

> #lang scribble/doc

The last one introduces the smallest number of typesetting bindings in the document body. Using scribble/base after #lang is the same as using scribble/doc plus (require scribble/base), and using scribble/manual after #lang is the same as using scribble/doc plus (require scribble/manual).

Besides making the file a module, each of the #lang declarations selects the Scribble reader (instead of the usual Racket reader), and it starts the body of the file in “text” mode. The reader layer mostly leaves text alone, but @-forms escape to S-expression mode.

A module written as

#lang scribble/doc
@(require scribble/manual)
@(define to-be "To Be")
@title{@|to-be| or Not @|to-be|}
@bold{That} is the question.
Whether 'tis nobler...

reads as

> (module ‹name› scribble/doc
> (require scribble/manual)
> "\n"
> (define to-be "To Be") "\n"
> "\n"
> (title to-be " or Not " to-be) "\n"
> "\n"
> (bold "That") " is the question." "\n"
> "Whether 'tis nobler..." "\n")

As shown in this example, the read result is a module whose content mingles text and definitions. The scribble/doc language lifts definitions, requires, and provides to the beginning of the module, while everything else is collected into a document bound to the provided identifier doc. That is, the module is transformed to something like this:

> (module ‹name› racket/base
> (require scribble/decode
> scribble/manual)
> (define to-be "To Be")
> (define doc
> (decode
> "\n" "\n" "\n"
> (title to-be " or Not " to-be) "\n"
> "\n"
> (bold "That") " is the question." "\n"
> "Whether 'tis nobler..." "\n"))
> (provide doc))

The decode function produces a part structure instance that represents the document. To build the part instance, it inspects its arguments to find a title-decl value created by title to name the part, part-start values created by section to designate sub-parts, etc.

A part is the input to a rendering back-end, such as the HTML renderer. All renderers recognize a fixed structure hierarchy: the content of a part is a flow, which is a sequence of flow elements, such as paragraphs and tables; a table, in turn, consists of a list of list of flows; a paragraph is a list of elements, which can be instances of the element structure type, plain strings, or certain special symbols.

The value bound to doc in the example above is something like

> (make-part ....
> (list "To Be" " or Not " "To Be") ; title
> ....
> (make-flow
> (list
> (make-paragraph
> (list (make-element 'bold (list "That"))
> " is the question." "\n"
> "Whether " 'rsquo "tis nobler..."))))
> ....)

Notice that the ' in the input’s 'tis has turned into 'rsquo (rendered as a curly apostrophe). The conversion to use 'rsquo was performed by decode via decode-flow via decode-paragraph via decode-content via decode-string.

In contrast, (make-element 'bold (list "That")) was produced by the bold function. The decode operation is a function, not a syntactic form, and so bold has control over its argument before decode sees the result. Also, decoding traverses only immediate string arguments.

As it turns out, bold also decodes its argument, because the bold function is implemented as

> (define (bold . strs)
> (make-element 'bold (decode-content strs)))

The verbatim function, however, does not decode its content, and instead typesets its text arguments directly.

A document module can construct elements directly using make-element, but normally functions like bold and verbatim are used to construct them. In particular, the scribble/manual library provides many functions and forms to typeset elements and flow elements.

The part structure hierarchy includes built-in element types for setting hyperlink targets and references. Again, this machinery is normally packaged into higher-level functions and forms, such as secref, defproc, and racket.

#### 6.1.2 Layer Roadmap🔗ℹ

Working roughly from the bottom up, the Scribble layers are:

- scribble/reader: A reader that extends the syntax of Racket with @-forms for conveniently embedding a mixin of text and escapes. See @ Syntax.

- scribble/core: A set of document datatypes and utilities that define the basic layout and processing of a document. For example, the part datatype is defined in this layer. See Structures And Processing.

- scribble/base-render with scribble/html-render, scribble/latex-render, or scribble/text-render: A base renderer and mixins that generate documents in various formats from instances of the scribble/struct datatypes. See Renderers.

- scribble/decode: Processes a stream of text, section-start markers, etc. to produce instances of the scribble/core datatypes. See Decoding Text.

- scribble/doclang: A language to be used for the initial import of a module; processes the module top level through scribble/decode, and otherwise provides all of racket/base. See Document Language.

- scribble/doc: A language that combines scribble/reader with scribble/doclang. See Document Reader.

- scribble/base: A library of basic document operators—such as title, section, and secref—for use with scribble/decode and a renderer. This library name also can be used as a language, where it combines scribble/doc with the exports of scribble/base. See Base Document Format.

- scribble/racket: A library of functions for typesetting Racket code. See Racket. These functions are not normally used directly, but instead used through scribble/manual.

- scribble/manual: A library of functions for writing Racket documentation; re-exports scribble/base. Also, the scribble/manual-struct library provides types for index-entry descriptions created by functions in scribble/manual. See Manual Forms.

- scribble/eval: A library of functions for evaluating code at document-build time, especially for showing examples. See Evaluation and Examples.

- scribble/bnf: A library of support functions for writing grammars. See BNF Grammars.

- scribble/xref: A library of support functions for using cross-reference information, typically after a document is rendered (e.g., to search). See Cross-Reference Utilities.

- scribble/text: A language that uses scribble/reader preprocessing text files.

The scribble command-line utility generates output with a specified renderer. More specifically, the executable installs a renderer, loads the modules specified on the command line, extracts the doc export of each module (which must be an instance of part), and renders each—potentially with links that span documents.

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