[HPSG-L] app for teaching phrase structure diagramming?

[Stephen Wechsler]

Does anyone know of an app for teaching phrase structure analysis?  What I
am looking for is a program in which the student/user is given a sentence
of a language (and perhaps a set of PS rules); the user makes a phrase
structure diagram of the sentence, and the app indicates whether the
diagram is correct or not, where correctness is determined by what the
teacher has programmed into it.

Thanks in advance for any pointers.

--Steve

Stephen Wechsler
Dept. of Linguistics
The University of Texas