From c15edae4532f53e7e5bac9dae125c360d93f848d Mon Sep 17 00:00:00 2001
From: Adrian Kummerlaender
Date: Sat, 21 Feb 2015 17:27:52 +0100
Subject: Separated Turing machine implementation into components * i.e.
 separate namespaces and headers for _Tape_ and _State_ functions * `void` is
 now used as the `BLANK` field value

---
 example/turing/src/machine.h | 98 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 98 insertions(+)
 create mode 100644 example/turing/src/machine.h

(limited to 'example/turing/src/machine.h')

diff --git a/example/turing/src/machine.h b/example/turing/src/machine.h
new file mode 100644
index 0000000..2404d9a
--- /dev/null
+++ b/example/turing/src/machine.h
@@ -0,0 +1,98 @@
+#ifndef TYPEASVALUE_EXAMPLE_TURING_MACHINE_H_
+#define TYPEASVALUE_EXAMPLE_TURING_MACHINE_H_
+
+#include "conditional/cond.h"
+
+#include "state.h"
+#include "tape.h"
+
+namespace machine {
+
+// (define (simulate transition tape state position)
+//   (if (= state FINAL)
+//     tape
+//     (let* ((current_symbol (readSymbol position tape))
+//            (current_state  (transition state current_symbol))
+//            (direction      (nth MOVE  current_state))
+//            (next_symbol    (nth WRITE current_state))
+//            (next_state     (nth NEXT  current_state))
+//            (next_position  (cond ((= direction RIGHT) (+ position 1))
+//                                  ((= direction LEFT)  (- Position 1))
+//                                  (else                position))))
+//       (simulate transition
+//                 (writeSymbol position next_symbol tape)
+//                 next_state,
+//                 next_position)))
+template <
+	template<typename, typename> class Transition,
+	typename                           State,
+	typename                           Tape,
+	typename                           Position
+>
+class simulate {
+	private:
+		using current_symbol = tape::readSymbol<Position, Tape>;
+		using current_state  = Transition<State, current_symbol>;
+
+		using direction      = tav::Nth<state::field::MOVE,  current_state>;
+
+		using next_symbol    = tav::Nth<state::field::WRITE, current_state>;
+		using next_state     = tav::Nth<state::field::NEXT,  current_state>;
+		using next_position  = tav::Cond<
+			tav::Branch<
+				tav::IsEqualValue<direction, tav::Char<'R'>>,
+				tav::Add<Position, tav::Size<1>>
+			>,
+			tav::Branch<
+				tav::IsEqualValue<direction, tav::Char<'L'>>,
+				tav::Substract<Position, tav::Size<1>>
+			>,
+			tav::Else<
+				Position
+			>
+		>;
+
+		static_assert(
+			tav::Not<tav::LowerThan<next_position, tav::Size<0>>>::value,
+			"next position out of bounds"
+		);
+
+	public:
+		using type = tav::Eval<simulate<
+			Transition,
+			next_state,
+			tape::writeSymbol<Position, next_symbol, Tape>,
+			next_position
+		>>;
+};
+
+template <
+	template<typename, typename> class Transition,
+	typename                           Tape,
+	typename                           Position
+>
+struct simulate<Transition, void, Tape, Position> {
+	typedef Tape type;
+};
+
+// (define (run program state tape position)
+//   (simulate (transition program)
+//             tape
+//             state
+//             position))
+template <
+	typename Program,
+	typename State,
+	typename Tape,
+	typename Position
+>
+using run = tav::Eval<simulate<
+	state::transition<Program>::template state,
+	State,
+	Tape,
+	Position
+>>;
+
+}
+
+#endif // TYPEASVALUE_EXAMPLE_TURING_MACHINE_H_
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