2 files changed, 112 insertions, 0 deletions
diff --git a/prolog/problems/denotational_semantics/algol_for_3/common.py b/prolog/problems/denotational_semantics/algol_for_3/common.py
new file mode 100644
index 0000000..3917aa6
--- /dev/null
+++ b/prolog/problems/denotational_semantics/algol_for_3/common.py
@@ -0,0 +1,93 @@
+id = 178
+group = 'denotational_semantics'
+number = 85
+visible = True
+facts = None
+
+solution = '''\
+algol_for(fun(S0,S,apply178([printout=[]|S0],S,Minstructs))) -->
+  [begin], instructs178(Minstructs), [end].
+
+instructs178(Minstr) --> instr178(Minstr).
+instructs178(fun(S0,S,
+  (apply178(S0,S1,Minstr),
+   apply178(S1,S,Minstructs)))) 
+  --> 
+  instr178(Minstr), instructs178(Minstructs).
+
+instr178(Massign) --> assign178(Massign).
+instr178(fun(S0,[printout = L1|S1],
+  (memb(X = V,S0),
+   del(printout = L0,S0,S1),
+   conc(L0,[V],L1))))
+  -->
+  [print(X)].
+instr178(fun(S0,S,
+  loop178(S0,Mcond,Minstructs,S)))
+  -->
+  [while], cond178(Mcond), [do,begin], instructs178(Minstructs), [end].
+instr178(fun(S0, S,
+  (apply178(S0, S1, Minit),
+   for178(S1, Mcond, Mstep, Mbody, S))))
+  -->
+  [for], assign178(Minit), [&], cond178(Mcond), [&], assign178(Mstep), [do, begin], instructs178(Mbody), [end].
+
+assign178(fun(S0,[X = Value|S1], 
+  (apply178(S0,Value,Mexpr),
+   del(X = _,S0,S1)))) 
+  -->
+  var178(X), [:=], expr178(Mexpr).
+
+cond178( fun( S, TruthVal,
+  (apply178(S,Val1,ME1),
+   apply178(S,Val2,ME2),
+   (Val1 < Val2,!,TruthVal = true ; TruthVal = false))))
+  -->
+  expr178(ME1), [<], expr178(ME2).
+
+var178(X) --> [X], {atom(X)}.
+
+expr178(fun(S,Value,eval(Expr,S,Value))) -->
+  [Expr].
+
+apply178(In, Out, fun(In, Out, Goals)) :-
+  call(Goals).
+
+loop178( State0, Mcond, _, State0) :-
+  apply178( State0, false, Mcond), !.
+loop178( S0, Mcond, MBody, S) :- 
+  copy_term( MBody, MBodyCopy),
+  apply178( S0, S1, MBody),
+  loop178( S1, Mcond, MBodyCopy, S).
+
+for178(S0, Mcond, _, _, S0) :-
+  apply178(S0, false, Mcond), !.
+for178(S0, Mcond, Mstep, Mbody, S) :-
+  copy_term(Mbody, Mbody2),
+  copy_term(Mstep, Mstep2),
+  apply178(S0, S1, Mbody),
+  apply178(S1, S2, Mstep),
+  for178(S2, Mcond, Mstep2, Mbody2, S).
+
+eval178( N, _, N) :-
+  number178( N), !.
+eval178( X, State, Val) :- % A program variable
+  atom( X), !, 
+  memb( X = Val, State). 
+eval178( E1 + E2, State, Val) :- !,
+  eval178( E1, State, V1),
+  eval178( E2, State, V2),
+  Val is V1 + V2.
+eval178( E1 - E2, State, Val) :- !,
+  eval178( E1, State, V1),
+  eval178( E2, State, V2),
+  Val is V1 - V2.
+eval178( E1 * E2, State, Val) :- !,
+  eval178( E1, State, V1),
+  eval178( E2, State, V2),
+  Val is V1 * V2.
+eval178( E1 / E2, State, Val) :- !,
+  eval178( E1, State, V1),
+  eval178( E2, State, V2),
+  Val is V1 /  V2.
+'''
diff --git a/prolog/problems/denotational_semantics/algol_for_3/en.py b/prolog/problems/denotational_semantics/algol_for_3/en.py
new file mode 100644
index 0000000..3578b71
--- /dev/null
+++ b/prolog/problems/denotational_semantics/algol_for_3/en.py
@@ -0,0 +1,19 @@
+id = 178
+name = 'algol_for/3'
+slug = 'interpreter for mini-algol with for-statement'
+
+description = '''\
+<p>Extend the given DCG for mini-algol to support the for-statement. Example:</p>
+<pre>
+  % for a := 0 & a < 5 & a := a + 1 do
+  % begin
+  %   print(a)
+  % end
+  ?- _Program = [begin,for,a,:=,0,&,a,<,5,&,a,:=,a+1,do,begin,print(a),end,end],
+      algol_for(_F, _Program, []),
+      apply([a=2], Output, _F).
+    Output = [a=5,printout=[0,1,2,3,4]].
+</pre>
+'''
+
+hint = {}