tasks a-s

Task/Parsing-RPN-calculator-algorithm/Prolog/parsing-rpn-calculator-algorithm.pro

@@ -0,0 +1,47 @@
+rpn(L) :-
+	writeln('Token  Action                             Stack'),
+	parse(L, [],[X] ,[]),
+	format('~nThe final output value is ~w~n', [X]).
+
+% skip spaces
+parse([X|L], St) -->
+	{char_type(X, white)},
+	parse(L, St).
+
+% detect operators
+parse([Op|L], [Y, X | St]) -->
+	{ is_op(Op, X, Y, V),
+	  writef('    %s', [[Op]]),
+	  with_output_to(atom(Str2), writef('Apply %s on top of stack', [[Op]])),
+	  writef('  %35l', [Str2]),
+	  writef('%w\n', [[V | St]])},
+	parse(L, [V | St]).
+
+% detect number
+parse([N|L], St) -->
+	{char_type(N, digit)},
+	parse_number(L, [N], St).
+
+% string is finished
+parse([], St) --> St.
+
+% compute numbers
+parse_number([N|L], NC, St) -->
+	{char_type(N, digit)},
+	parse_number(L, [N|NC], St).
+
+parse_number(S, NC, St) -->
+	{ reverse(NC, RNC),
+	  number_chars(V, RNC),
+	  writef('%5r', [V]),
+	  with_output_to(atom(Str2), writef('Push num %w on top of stack', [V])),
+	  writef('  %35l', [Str2]),
+	  writef('%w\n', [[V | St]])},
+	parse(S, [V|St]).
+
+% defining operations
+is_op(42, X, Y, V) :-	V is X*Y.
+is_op(43, X, Y, V) :-	V is X+Y.
+is_op(45, X, Y, V) :-	V is X-Y.
+is_op(47, X, Y, V) :-	V is X/Y.
+is_op(94, X, Y, V) :-	V is X**Y.