GF online editor for simple multilingual grammars

About

Traditionally, GF grammars are created in a text editor and tested in the GF shell. Text editors know very little (if anything) about the syntax of GF grammars, and thus provide little guidance for novice GF users. Also, the grammar author has to download and install the GF software on his/her own computer.

In contrast, the GF online editor for simple multilingual grammars is available online, making it easier to get started. All that is needed is a reasonably modern web browser. Even Android and iOS devices can be used.

The editor also guides the grammar author by showing a skeleton grammar file and hinting how the parts should be filled in. When a new part is added to the grammar, it is immediately checked for errors.

Editing operations are accessed by clicking on editing symbols embedded in the grammar display: +=Add an item, ×=Delete an item, %=Edit an item. These are revealed when hovering over items. On touch devices, hovering is in some cases simulated by tapping, but there is also a button at the bottom of the display to "Enabile editing on touch devices" that reveals all editing symbols.

In spite of its name, the editor runs entierly in the web browser, so once you have opened the web page, you can continue editing grammars even while you are offline.

Limitations

At the moment, the editor supports only a small subset of the GF grammar notation. Proper error checking is done for abstract syntax, but not (yet) for concrete syntax. The resource grammar library is not available.

The grammars created with this editor always consists of one file for the abstract syntax, and one file for each concrete syntax.

Abstract syntax

The supported abstract syntax corresponds to context-free grammars (no dependent types). The definition of an abstract syntax is limited to

a list of category names, Cat₁ ; ... ; Cat_n,
a list of functions of the form Fun : Cat₁ -> ... -> Cat_n,
and a start category.

Available editing operations:

Categories can be added, removed and renamed. When renaming a category, occurences of it in function types will be updated accordingly.
Functions can be added, removed and edited. Concrete syntaxes are updated to reflect changes.
Functions can be reordered using drag-and-drop.

Error checks:

Syntactically incorrect function definitions are refused.
Semantic problem such as duplicated definitions or references to undefined categories, are highlighted.

Concrete syntax

At the moment, concrete syntax definitions are limited to

parameter types, P = C₁ | ... |C_n,
linearization types for the categories in the abstract syntax,
operation definitions, op = expr,
and linearizations for the functions in the abstract syntax.

Available editing operations:

The LHSs of the linearization types and linearizations are determined by the abstract syntax and do not need to be entered manually. The RHSs can be edited.
Parameter types can be added, removed and edited.
Operation definitons can be added, removed and edited.
Definitions can be reordered (using drag-and-drop)

Error checks:

The RHSs in the concrete syntax are not checked for errors. Arbitrary strings can be entered.

Testing grammars

By pressing the Upload button, a grammar can be uploaded to the GF server. It will then be compiled with GF, and any errors not checked by the editor will be detected and reported. If the grammar is free from errors, the user can test the grammar by clicking on links to the online GF shell, the Minibar or the Translation Quiz.

Future work

This prototype gives an idea of how a web based GF grammar editor could work. We do not expect to create a full implementation of GF that runs in the web browser, but let the editor communicate with a server running GF.

By developing a GF server with an appropriate API, it should be possible to extend the editor to support a larger fragment of GF, to do proper error checking, and to allow grammars to be tested in the GF shell or the minibar.

Grammars are currently stored locally in the browser, but a future version could allow grammars to be stored "in the cloud", allowing the same grammars to be accessed from multiple devices.

Last modified: Wed Feb 23 17:37:16 CET 2011