commit 25005646e43f648d30e646588a497e46c7eb5752
Author: Sigma <git@sigma-star.io>
Date:   Sat Sep 14 21:57:10 2024 +0200

    Create turing.sql

diff --git a/turing.sql b/turing.sql
new file mode 100644
index 0000000..8967366
--- /dev/null
+++ b/turing.sql
@@ -0,0 +1,113 @@
+CREATE TABLE input (
+  input BYTEA
+);
+
+INSERT INTO input VALUES ('aabbbaa'::BYTEA || '\x00'::BYTEA);
+
+CREATE TABLE program (
+  state INT,
+  read INT,
+  next_state INT,
+  write INT,
+  move INT,
+  accept BOOL DEFAULT false,
+  reject BOOL DEFAULT false
+);
+
+INSERT INTO program VALUES 
+  -- search right
+  (000,        0  , 100,        0  , 0, false, false), -- input is empty; accept
+  (000, ASCII('a'), 011,        0  , 1, false, false),
+  (000, ASCII('b'), 016,        0  , 1, false, false),
+  
+  -- search right for 'a' 
+  (011,        0  , 012,        0  , -1, false, false), -- end found
+  (011, ASCII('a'), 011, ASCII('a'),  1, false, false),
+  (011, ASCII('b'), 011, ASCII('b'),  1, false, false),
+  
+  -- search right for 'a': verify value
+  (012,        0  , 100,        0  ,  0, false, false),
+  (012, ASCII('a'), 001,        0  , -1, false, false),
+  (012, ASCII('b'), 101,        0  ,  0, false, false), -- 1 expected, 2 found
+  
+  -- search right for 'b'
+  (016,        0  , 017,        0  , -1, false, false), -- end found
+  (016, ASCII('a'), 016, ASCII('a'),  1, false, false),
+  (016, ASCII('b'), 016, ASCII('b'),  1, false, false),
+  
+  -- search right for 'b': verify value
+  (017,        0  , 100,        0  ,  0, false, false),
+  (017, ASCII('a'), 101,        0  ,  0, false, false), -- 2 expected, 1 found
+  (017, ASCII('b'), 001,        0  , -1, false, false), 
+  
+  
+  -- search left
+  (001,        0  , 100,        0  ,  0, false, false), -- input is empty; accept
+  (001, ASCII('a'), 021,        0  , -1, false, false),
+  (001, ASCII('b'), 026,        0  , -1, false, false),
+    
+  -- search left for 'a' 
+  (021,        0  , 022,        0  ,  1, false, false), -- end found
+  (021, ASCII('a'), 021, ASCII('a'), -1, false, false),
+  (021, ASCII('b'), 021, ASCII('b'), -1, false, false),
+  
+  -- search left for 'a': verify value
+  (022,        0  , 100,        0  ,  0, false, false),
+  (022, ASCII('a'), 000,        0  ,  1, false, false),
+  (022, ASCII('b'), 101,        0  ,  0, false, false), -- 1 expected, 2 found
+  
+  -- search left for 'b'
+  (026,        0  , 027,        0  ,  1, false, false), -- end found
+  (026, ASCII('a'), 026, ASCII('a'), -1, false, false),
+  (026, ASCII('b'), 026, ASCII('b'), -1, false, false),
+  
+  -- search left for 'b': verify value
+  (027,        0  , 100,        0  ,  0, false, false),
+  (027, ASCII('a'), 101,        0  ,  0, false, false), -- 2 expected, 1 found
+  (027, ASCII('b'), 000,        0  ,  1, false, false), 
+  
+  
+  -- accept state
+  (100,        0  , 100,        0  ,  0, true, false),
+  (100, ASCII('a'), 100,        0  ,  0, true, false),
+  (100, ASCII('b'), 100,        0  ,  0, true, false),
+  
+  -- reject state
+  (101,        0  , 101,        0  ,  0, false, true),
+  (101, ASCII('a'), 101,        0  ,  0, false, true),
+  (101, ASCII('b'), 101,        0  ,  0, false, true)
+;
+
+
+WITH RECURSIVE run_state (iteration, state, position, band, accept, reject) AS (
+  SELECT 
+    0, 000, 0 , input, false, false
+  FROM input
+
+  UNION ALL
+  
+  SELECT 
+    run_state.iteration + 1,
+    program.next_state,
+    run_state.position + program.move,
+    set_byte(run_state.band, run_state.position, program.write),
+    program.accept,
+    program.reject
+  FROM run_state
+  INNER JOIN program
+    ON  program.state = run_state.state
+    AND program.read = get_byte(run_state.band, run_state.position)
+  WHERE 
+        NOT run_state.accept 
+    AND NOT run_state.reject
+)
+SELECT 
+  CASE
+    WHEN run.accept THEN 'Input was accepted in ' || run.iteration || ' iterations.'
+    WHEN run.reject THEN 'Input was rejected in ' || run.iteration || ' iterations.'
+    ELSE '[insert confused meme here]'
+  END
+FROM run_state AS run
+WHERE 
+     run.accept
+  OR run.reject;