Landon Curt Noll
d414b6d71f
Improved `all-run.sh` and `readme2index.sh` so that certain command line options (e.g., -p, -P, -u, -U ...) are only passed along to other tools if they are given on the command line. all-run.sh VERSION changed from "1.1.1 2024-01-19" to "1.1.2 2024-01-20", readme2index.sh VERSION changed from "1.1 2024-01-16" to "1.1.1 2024-01-20". Added `quick-readme2index.sh` that only calls `readme2index.sh` if the `index.html` is not a non-empty file, or of either `.winner.json` and/or `README.md` is newer than `index.html`. Updated all `index.html` files because the the file contains a comment that includes the newly modified readme2index.sh VERSION.
To build:
make
To use:
make -B [MACHINE=your_machine.h] [TAPE=your_tape.h] [X=[0|1|2|3|4|5|6|7|8|9]] [V=[0|1|2]] run
Try:
./try.sh
Judges' remarks:
This is something we were fearing all along: that the C preprocessor is Turing-complete even without conditionals and recursive file inclusion as some kind of a rewriting system. Now we have the proof!
Author's remarks:
Preprocessor Turing Engine
Features
- Turing machine runs in preprocessor
- universal (unlimited configurable states, symbols, and tape)
- no
#ifs or other conditional directives, only#defines - no recursive
#include - single compiler run (no repeated preprocessing)
- no variadic macros
- verbosity levels:
V=0(default) only prints the final tapeV=1additionally prints one tilde character per machine step (slow)V=2additionally prints details on each machine step (slow; generates large files)
- make target
runruns./progand filters a little statistics out of the verbose output X(defaults to 3) sets the maximum number of steps: M(X) ~ 8X
Limitations
If the machine does not halt after M(X) steps, you will see unexpanded
macros in the output.
Compiler warnings
If V=1 or V=2 is used, you may see "warning: string length is greater than the length '4095' ISO C99 compilers are required to support".
Programming
Implementing your own Turing machine is easy. Take a look at the supplied header files for examples.
Tape Symbols
Every symbol used (except _) must be explicitly declared using
#define sym_SYMBOL(sym, _SYMBOL) sym
Example:
#define sym_1(sym, _1) sym
Tape
The initial content of the tape must be defined in the tape header using a triple like:
#define tape ((((,),...l2), l1), c, (r1, (r2..., (,))))
l1,l2, ... are the symbols to the leftcis the symbol at the current positionr1,r2, ... are the symbols to the right
The empty pairs (,) represent the continuations of the tape, filled with
underscore symbols (_). They are expanded on demand.
State Machine
All transitions are defined in the machine header using the syntax
#define CURRENT_SCANNED (WRITE, MOVEMENT, NEXT)
where
CURRENTis the current state.SCANNEDis the symbol at the current position.- The whitespace before the parentheses is significant.
WRITEis the symbol to be written to the tape.MOVEMENTisLfor left,Rfor right; don't specify anything if you want no movement.NEXTis the next state.
There must be a state A defined, which becomes the initial state of the
machine.
To halt the machine, use the keyword break as in
#define A_1 (2, break)
Copyright and CC BY-SA 4.0 License:
This file is Copyright (c) 2023 by Landon Curt Noll. All Rights Reserved. You are free to share and adapt this file under the terms of this license:
Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0)
For more information, see: https://creativecommons.org/licenses/by-sa/4.0/