‘Hello world’ in literate Elm
Adding litvis attribute l
(or literate
) to elm
blocks in markdown automatically compiles and executes the code in real time. Attribute r
(or raw
) is the simplest way to see the result.
Simple litvis chart
A litvis code block with attribute v
(or visualize
) automatically renders the declared symbol using elm-vegalite
or elm-vega
.
Code referencing across blocks
By default, litvis code blocks share the same execution context, which means that an Elm symbol defined in one block and can be referenced in another block. Blocks can be placed in any order.
Code referencing with triple hat notation
Symbols from Elm code blocks can be referenced in any part of the markdown using triple hat notation (^^^
).
Code referencing with parameters
Triple hat references accept parametrized function calls, which makes it easy to combine text with graphics and produce families of related graphics. This means that small multiples and embedded graphics such as sparklines are straightforward.
Debugging Code
A litvis document that is being previewed is constantly checked for program validity. Any issues that are detected are displayed in the editing environment and help with debugging. If a visualization has been successfully rendered before the issue had occurred, its old preview is shown to avoid unwanted markup reflows.
Replacing v
with r
for raw
or j
for json
makes it possible to look into generated vega-lite specs.
This can help debugging more deeply embedded problems or for generating standard JSON Vega/Vega-Lite specifications.
Interaction
Adding interactive
to a code block with v
or a triple hat reference makes visualizations live if interaction is described within Spec
. User input controls can be added to the document, if desired.
Multiple execution contexts
Although a single Elm execution context may be sufficient in many litvis narratives, context isolation may be desired in some cases. A number of code block attributes such as context
, id
, follows
, isolated
and siding
enable fine-grained control of Elm symbol visibility, thus making it easier to accomplish certain tasks.
A siding
(or s
) is a shortcut for isolated follows=default
. This keyword makes previously defined symbols in default
context available within the code block, but avoids name clashes with any blocks later in the document.
Branching narratives
A litvis narrative can be split between multiple markdown documents, where each document follows
its parent. This enables routine use of parallel branching narratives that assemble and structure document trees. Each branch in a tree can represent alternative designs each with their own rationale or focus for analysis.
examples/features/branching/root.md > examples/features/branching/branchA.md > examples/features/branching/branchB.md
Narrative schemas
A litvis narrative can be linked to a set of YAML files, which define labels
, rules
and styling
.
These narrative schemas can be thought of as an analogue of schemas more usually found in declarative programming contexts such as JSON and XML schema.
The purpose of the schema is to provide a set of structured guidelines to assist in writing the narrative content around visualizations. This can be thought of as form of scaffolding to assist in the process of design exposition or reasoning. Schemas can be used to validate litvis documents.
Automatic code formatting
Litvis integrates with Prettier and its Elm plugin, which enables seamless document formatting as the narrative is being written. A file is automatically prettified on save or when the Format command is explicitly called. Formatting keeps litvis files in a readable and maintainable state, which eases collaboration and reduces distraction from the higher-level tasks.