"Thats the beauty of it. It doesn't *do* anything." ;)
On Thu, Mar 1, 2018 at 6:55 AM, Gary Briggs <chu...@icculus.org> wrote:
> Thanks to the help the other day with the strange concatentation result.
>
> I was referring to a BF interpreter I was working on, in pure SQLite SQL.
> Well, here it is, working.
>
> Hopefully no-one finds this useful,
> Gary
>
> WITH RECURSIVE
> program AS
> (SELECT '++++++++++[>+++++++>++++++++++>+++>+<<<<-]>++.>+.+++++++..+
> ++.>++.<<+++++++++++++++.>.+++.------.--------.>+.>.' AS p,
> '' AS input, 3 AS width
> ),
> jumpdepth AS
> (SELECT 0 AS idx, 0 AS jumpdepth, '' AS jumplist, NULL as jumpback,
> NULL AS direction, p || '0' AS p, width FROM program
> UNION ALL
> SELECT idx+1, CASE SUBSTR(p, idx+1, 1)
> WHEN '[' THEN jumpdepth+1
> WHEN ']' THEN jumpdepth-1
> ELSE jumpdepth END,
> CASE SUBSTR(p, idx+1, 1)
> WHEN '[' THEN SUBSTR('0000000' || (idx+1), -width) ||
> jumplist
> WHEN ']' THEN SUBSTR(jumplist,width+1)
> ELSE jumplist END,
> CASE SUBSTR(p, idx+1, 1)
> WHEN ']' THEN CAST(SUBSTR(jumplist,1,width) AS INTEGER)
> ELSE NULL END,
> CASE SUBSTR(p, idx+1, 1)
> WHEN '[' THEN 'L'
> WHEN ']' THEN 'R'
> ELSE NULL END,
> p, width
> FROM jumpdepth
> WHERE LENGTH(p)>=idx),
> jumptable(a,b,dir) AS
> (SELECT idx,jumpback,'L' FROM jumpdepth WHERE jumpback IS NOT NULL
> UNION ALL
> SELECT jumpback,idx+1,'R' FROM jumpdepth WHERE jumpback IS NOT
> NULL),
> bf(ep, p, width, defaulttapeentry, ip, dp, instruction, output, input,
> tape) AS
> (SELECT 0, p, width, SUBSTR('0000000', -width), 1, 1, '', '',
> input, SUBSTR('000000', -width)
> FROM program
> UNION ALL
> SELECT ep+1, p, width, defaulttapeentry, CASE WHEN jumptable.b IS
> NOT NULL AND
> ((dir='R' AND CAST(SUBSTR(tape, width*(dp-1)+1, width) AS
> INTEGER)=0)
> OR
> (dir='L' AND CAST(SUBSTR(tape, width*(dp-1)+1, width) AS
> INTEGER)!=0)) THEN jumptable.b
> ELSE ip+1 END,
> CASE SUBSTR(p, ip, 1)
> WHEN '>' THEN dp+1
> WHEN '<' THEN MAX(dp-1,1)
> ELSE dp END,
> SUBSTR(p, ip, 1),
> CASE WHEN SUBSTR(p, ip, 1)='.' THEN (output || CHAR(SUBSTR(tape,
> (dp-1)*width+1, width))) ELSE output END,
> CASE WHEN SUBSTR(p, ip, 1)=',' THEN SUBSTR(input, 2) ELSE input
> END,
> CASE SUBSTR(p, ip, 1)
> WHEN '<' THEN CASE WHEN dp=1 THEN defaulttapeentry || tape
> ELSE tape END
> WHEN '>' THEN CASE WHEN dp*width=LENGTH(tape) THEN tape ||
> defaulttapeentry ELSE tape END
> WHEN '+' THEN SUBSTR(tape,1,width*(dp-1)) ||
> SUBSTR('0000000' || (CAST(SUBSTR(tape,width*(dp-1)+1,width) AS
> INTEGER)+1), -width) || SUBSTR(tape,width*dp+1)
> WHEN '-' THEN SUBSTR(tape,1,width*(dp-1)) ||
> SUBSTR('0000000' || (CAST(SUBSTR(tape,width*(dp-1)+1,width) AS
> INTEGER)-1), -width) || SUBSTR(tape,width*dp+1)
> WHEN ',' THEN SUBSTR(tape,1,width*(dp-1)) ||
> SUBSTR('0000000' || (UNICODE(SUBSTR(input,1,1))), -width) ||
> SUBSTR(tape,width*(dp+1))
> ELSE tape END
> FROM bf LEFT JOIN jumptable ON jumptable.a=ip WHERE LENGTH(p) >= ip)
> SELECT output FROM bf ORDER BY ep DESC LIMIT 1;
>
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