Hdrug is an environment to develop logic grammars / parsers / generators for natural languages. The package is written in Sicstus Prolog version 3 and uses library(tcltk) to implement its user interface. Tcl/Tk is a powerful script language to develop applications for the X-windows environment.
Hdrug offers various tools to visualize lexical entries, grammar rules, definite-clause definitions, parse trees, feature structures, lexical- rule- and type-hierarchies, graphs of the comparison of different parsers on a corpus of test sentences etc., in a Tk widget, LaTeX/DVI format, and the Clig system.
The package comes with a number of example grammars, including the grammars to be found in the distribution of the ALE system.
Hdrug allows for easy comparison of different parsers/generators; it has extensive possibilities to compile feature equations into Prolog terms; it can produce graphical (Tk), and ordinary Prolog output of trees, feature structures, Prolog terms (and combinations thereof), plotted graphs of statistical information, and tables of statistical information. Etc. Etc.
Using just menu's and buttons it is possible to parse sentences, generate sentences from logical form representations, view the parse trees that are derived by the parser or generator, change a particular version of the parser on the fly, compare the results of parsing the same sentence(s) with a set of different parsers, etc.
HDRUG was designed and implemented by Gertjan van Noord. The HDRUG
home-page is http://www.let.rug.nl/~vannoord/Hdrug/.