External module Languages

When extending Wrattler, you have a range of options from creating (just) a new server-side execution runtime to implementing custom user interface for a cell. The types in this module let you imlement new language plugins that do some interesting work directly in the web browser.

• LanguagePlugin is the main type that you need to implement if you want to add new language to Wrattler. The type is responsible for parsing, binding (i.e. the construction of a dependnecy graph), evaluation and also user interface.

• Block is produced by parsing source code. Each language can define its own type and store either the code itself or some parsed abstract syntax tree.

Constructing dependency graph

The following types are related to the bind operation of a LanguagePlugin:

• BindingContext provides the language plugin with a cache for reusing past graph nodes, variables that are in scope from previous cells (the ScopeDictionary type) and also source files (e.g. *.py) that were imported in previous cells (the Resource type).

• BindingResult is the result of bind. It includes one graph node representing the whole code cell and an array representing exported data frames. It can also return new source files that should be automatically loaded in further cells (as values of the Resource type).

Evaluating graph node values

The following types are related to the eval operation of a LanguagePlugin:

• EvaluationContext provides the evaluator with files that are imported in previous cells.

• EvaluationResult represents the result of evaluation. This can be either EvaluationFailure, consisting of an array of errors, or EvaluationSuccess consisting of a Value that should be stored with the graph node.

Implementing custom editors

The following types are needed when implementing custom editor for a new language:

• Editor is the main type to implement. Editors in Wrattler follow the Elm architecture. They expose render function, which generates virtual HTML nodes based on the current state and update function, which is used to update the state when an event happens.

• Editor for each language has its own type of events. The type used to represent state needs to implement the EditorState interface.

• BlockState is passed to render when rendering a notebook. It stores the EditorState of the given editor and information about dependency graph nodes corresponding to the cell.

• EditorContext is passed as an extra parameter to render. It provides operations for triggering events (to be called from JavaScript event handlers), rebinding and triggering evaluation.