```    1/*
2A prefix parser for a probabilistic left-corner grammar.
3From
4T. Sato, P. Meyer, Tabling for infinite probability computation, in:
5Intnational Confence on Logic Programming, Vol. 17 of LIPIcs, 2012,
6pp.  348-358.
7T. Sato, P. Meyer, Infinite probability computation by cyclic explanation
8graphs, Theory and Practice of Logic Programming 14 (2014) 909-937.
9doi:10.1017/S1471068413000562.
10*/
11
12
13:- use_module(library(mcintyre)).   14
15:- if(current_predicate(use_rendering/1)).   16:- use_rendering(c3).   17:- endif.   18
19:- mc.   20
23% S->SS
24% S->a
25% S->b
26pre_plc(Ws) :- g_call(['S'] ,Ws,[], [],_Der).
27
28g_call([],L,L,Der,Der).
29
30g_call([G|R], [G|L],L2,Der0,Der) :- % shift
31  terminal(G),
32  g_call(R,L,L2,Der0,Der).
33
34g_call([G|_R], [Wd|L] ,[],Der0,Der) :-
35  \+ terminal(G),
36  first(G,Der0,Wd),
37  lc_call(G,Wd,L,[],[first(G,Wd)|Der0],Der). % pseudo success
38
39g_call([G|R], [Wd|L] ,L2,Der0,Der) :-
40  \+ terminal(G),
41  first(G,Der0,Wd),
42  lc_call(G,Wd,L,L1,[first(G,Wd)|Der0],Der1),
43  g_call(R,L1,L2,Der1,Der).
44
45lc_call(G,B,L,L1,Der0,Der) :- % attach
46  lc(G,B,Der0,rule(G, [B|RHS2])),
47  attach_or_project(G,Der0,attach),
48  g_call(RHS2,L,L1,[lc(G,B,rule(G, [B|RHS2])),attach|Der0],Der).
49
50lc_call(G,B,L,L2,Der0,Der) :- % project
51  lc(G,B,Der0,rule(A, [B|RHS2])),
52  attach_or_project(G,Der0,project),
53  g_call(RHS2,L,L1,[lc(G,B,rule(A, [B|RHS2])),project|Der0],Der1),
54  lc_call(G,A,L1,L2,Der1,Der).
55
56lc_call(G,B,L,L2,Der0,Der) :-
57  \+ lc(G,B,Der0,rule(G,[B|_])),
58  lc(G,B,Der0,rule(A, [B|RHS2])),
59  g_call(RHS2,L,L1,[lc(G,B,rule(A, [B|RHS2]))|Der0],Der1),
60  lc_call(G,A,L1,L2,Der1,Der).
61
62
63attach_or_project(A,Der,Op) :-
64  lc(A,A,Der,_),
65  attach(A,Der,Op).
66
67attach_or_project(A,Der,attach) :-
68  \+ lc(A,A,Der,_).
69
70
71lc('S','S',_Der,rule('S',['S','S'])).
72
73lc('S',a,_Der,rule('S',[a])).
74
75lc('S',b,_Der,rule('S',[b])).
76
77first('S',Der,a):0.5; first('S',Der,b):0.5.
78
79
80attach('S',Der,attach):0.5; attach('S',Der,project):0.5.
81
82terminal(a).
83terminal(b).
84
85
86
?- `mc_prob(pre_plc([a,b]),P)`. what is the probability of sentence [a,b]? % expecte result ~ 0.0326