From bbcb29a202436fc0e222e187f1fadf0b1f305465 Mon Sep 17 00:00:00 2001
From: Timotej Lazar <timotej.lazar@fri.uni-lj.si>
Date: Sun, 22 May 2016 17:48:30 +0200
Subject: Prolog: update denotational_semantics problems

---
 prolog/problems/algol/algol_if_3/common.py | 85 ++++++++++++++++++++++++++++++
 prolog/problems/algol/algol_if_3/en.py     | 19 +++++++
 2 files changed, 104 insertions(+)
 create mode 100644 prolog/problems/algol/algol_if_3/common.py
 create mode 100644 prolog/problems/algol/algol_if_3/en.py

(limited to 'prolog/problems/algol/algol_if_3')

diff --git a/prolog/problems/algol/algol_if_3/common.py b/prolog/problems/algol/algol_if_3/common.py
new file mode 100644
index 0000000..6678743
--- /dev/null
+++ b/prolog/problems/algol/algol_if_3/common.py
@@ -0,0 +1,85 @@
+id = 177
+number = 20
+visible = False
+facts = None
+
+solution = '''\
+algol_if(fun(S0,S,apply177([printout=[]|S0],S,Minstructs))) -->
+  [begin], instructs177(Minstructs), [end].
+
+instructs177(Minstr) --> instr177(Minstr).
+instructs177(fun(S0,S,
+  (apply177(S0,S1,Minstr),
+   apply177(S1,S,Minstructs))))
+  -->
+  instr177(Minstr), instructs177(Minstructs).
+
+instr177(Massign) --> assign177(Massign).
+instr177(fun(S0,[printout = L1|S1],
+  (memb(X = V,S0),
+   del(printout = L0,S0,S1),
+   conc(L0,[V],L1))))
+  -->
+  [print(X)].
+instr177(fun(S0,S,
+  loop177(S0,Mcond,Minstructs,S)))
+  -->
+  [while], cond177(Mcond), [do,begin], instructs177(Minstructs), [end].
+instr177(fun(S0, S,
+  (apply177(S0, true, Mcond), !,
+   apply177(S0, S, MinstructsA)
+   ;
+   apply177(S0, S, MinstructsB))))
+  -->
+  [if], cond177(Mcond), [then], instructs177(MinstructsA), [else], instructs177(MinstructsB), [end].
+
+assign177(fun(S0,[X = Value|S1],
+  (apply177(S0,Value,Mexpr),
+   del(X = _,S0,S1))))
+  -->
+  var177(X), [:=], expr177(Mexpr).
+
+cond177( fun( S, TruthVal,
+  (apply177(S,Val1,ME1),
+   apply177(S,Val2,ME2),
+   (Val1 < Val2,!,TruthVal = true ; TruthVal = false))))
+  -->
+  expr177(ME1), [<], expr177(ME2).
+
+var177(X) --> [X], {atom(X)}.
+
+expr177(fun(S,Value,eval(Expr,S,Value))) -->
+  [Expr].
+
+apply177(In, Out, fun(In, Out, Goals)) :-
+  call(Goals).
+
+loop177( State0, Mcond, _, State0) :-
+  apply177( State0, false, Mcond), !.
+loop177( S0, Mcond, MBody, S) :- 
+  copy_term( MBody, MBodyCopy),
+  apply177( S0, S1, MBody),
+  loop177( S1, Mcond, MBodyCopy, S).
+
+eval177( N, _, N) :-
+  number177( N), !.
+eval177( X, State, Val) :- % A program variable
+  atom( X), !,
+  memb( X = Val, State).
+eval177( E1 + E2, State, Val) :- !,
+  eval177( E1, State, V1),
+  eval177( E2, State, V2),
+  Val is V1 + V2.
+eval177( E1 - E2, State, Val) :- !,
+  eval177( E1, State, V1),
+  eval177( E2, State, V2),
+  Val is V1 - V2.
+eval177( E1 * E2, State, Val) :- !,
+  eval177( E1, State, V1),
+  eval177( E2, State, V2),
+  Val is V1 * V2.
+eval177( E1 / E2, State, Val) :- !,
+  eval177( E1, State, V1),
+  eval177( E2, State, V2),
+  Val is V1 /  V2.
+'''
diff --git a/prolog/problems/algol/algol_if_3/en.py b/prolog/problems/algol/algol_if_3/en.py
new file mode 100644
index 0000000..bd5b732
--- /dev/null
+++ b/prolog/problems/algol/algol_if_3/en.py
@@ -0,0 +1,19 @@
+name = 'algol_if/3'
+slug = 'interpreter for mini-algol with if-statement'
+
+description = '''\
+<p>Extend the given DCG for mini-algol to support the if-statement. You can assume that both branches are present in every if-statement. Example:</p>
+<pre>
+% if a < b then
+%   print(a)
+% else
+%   print(b)
+% end
+?- _Program = [begin,if,a,<,b,then,print(a),else,print(b),end,end],
+    algol_if(_F, _Program, []),
+    apply([a=3,b=5], Output, _F).
+  Output = [a=3,b=5,printout=[3]].
+</pre>
+'''
+
+hint = {}
-- 
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