maxwell-10% prolog
C-Prolog version 1.5

| ?- [nlp].
nlp consulted 440 bytes 1.98682e-09 sec.

yes

| ?- trace.

yes

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

   (1) 1 Call: phrase(sentence,[boys,sing]) ? 
   (2) 2 Call: _65635=..[sentence,[boys,sing],[]] ? 
   (2) 2 Exit: sentence([boys,sing],[])=..[sentence,[boys,sing],[]]
   (3) 2 Call: sentence([boys,sing],[]) ? 
   (4) 3 Call: noun_phrase([boys,sing],_65662) ? 
   (5) 4 Call: c([boys,sing],boys,_65662) ? 
   (5) 4 Exit: c([boys,sing],boys,[sing])
   (4) 3 Exit: noun_phrase([boys,sing],[sing])
   (6) 3 Call: verb_phrase([sing],[]) ? 
   (7) 4 Call: c([sing],sing,[]) ? 
   (7) 4 Exit: c([sing],sing,[])
   (6) 3 Exit: verb_phrase([sing],[])
   (3) 2 Exit: sentence([boys,sing],[])
   (1) 1 Exit: phrase(sentence,[boys,sing])

yes

| ?- halt.

[ Prolog execution halted ]

maxwell-10%