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|
id = 178
number = 30
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.
'''
initial = '''\
% program
algol_for(fun(S0, S, apply([printout=[]|S0], S, Minstructs))) -->
[begin], instructs(Minstructs), [end].
% sequence of instructions
instructs(Minstr) --> instr(Minstr).
instructs(fun(S0,S,
(apply(S0,S1,Minstr),
apply(S1,S,Minstructs))))
-->
instr(Minstr), instructs(Minstructs).
% statement (instruction)
instr(Massign) --> assign(Massign).
% put the current value of a variable into the output list
instr(fun(S0, [printout = L1|S1],
(memb(X = V,S0),
del(printout = L0, S0, S1),
conc(L0, [V], L1))))
-->
[print(X)].
% while-loop
instr(fun(S0, S,
loop(S0, Mcond, Minstructs, S)))
-->
[while], cond(Mcond), [do, begin], instructs(Minstructs), [end].
% assignment statement
assign(fun(S0, [X = Value|S1],
(apply(S0, Value, Mexpr),
del(X = _, S0, S1))))
-->
var(X), [':='], expr(Mexpr).
% conditional expression
cond(fun(S, TruthVal,
(apply(S, Val1, ME1),
apply(S, Val2, ME2),
(Val1 < Val2, !, TruthVal = true ; TruthVal = false))))
-->
expr(ME1), ['<'], expr(ME2).
% variable
var(X) --> [X], { atom(X) }.
% expression
expr(fun(S, Value, eval(Expr, S, Value))) -->
[Expr]. % Expr is a Prolog arithmetic expression, e.g. x + 2*y + 3
% helper predicates
% function call
apply(In, Out, fun(In, Out, Goals)):-
call(Goals).
% loop
loop(State0, Mcond, _, State0) :-
apply(State0, false, Mcond), !. % condition is false
loop(S0, Mcond, MBody, S) :-
copy_term(MBody, MBodyCopy), % copy goals
apply(S0, S1, MBody), % run loop body
loop(S1, Mcond, MBodyCopy, S). % next iteration
% expression evaluation
eval(N, _, N) :-
number(N), !.
eval(X, State, Val) :- % a program variable
atom(X), !,
memb(X = Val, State).
eval(E1 + E2, State, Val) :- !,
eval(E1, State, V1),
eval(E2, State, V2),
Val is V1 + V2.
eval(E1 - E2, State, Val) :- !,
eval(E1, State, V1),
eval(E2, State, V2),
Val is V1 - V2.
eval(E1 * E2, State, Val) :- !,
eval(E1, State, V1),
eval(E2, State, V2),
Val is V1 * V2.
eval(E1 / E2, State, Val) :- !,
eval(E1, State, V1),
eval(E2, State, V2),
Val is V1 / V2.
'''
|
