maxwell-10% prolog
C-Prolog version 1.5

| ?- [nlp].
nlp consulted 440 bytes 0.0166667 sec.

yes

| ?- trace.

yes

| ?- sentence([boys,sing],[]).

   (1) 1 Call: sentence([boys,sing],[]) ? 
   (2) 2 Call: noun_phrase([boys,sing],_65637) ? 
   (3) 3 Call: c([boys,sing],boys,_65637) ? 
   (3) 3 Exit: c([boys,sing],boys,[sing])
   (2) 2 Exit: noun_phrase([boys,sing],[sing])
   (4) 2 Call: verb_phrase([sing],[]) ? 
   (5) 3 Call: c([sing],sing,[]) ? 
   (5) 3 Exit: c([sing],sing,[])
   (4) 2 Exit: verb_phrase([sing],[])
   (1) 1 Exit: sentence([boys,sing],[])

yes

| ?- halt.

[ Prolog execution halted ]

maxwell-10%