Lib.rs

Idea

This is a simulation of pushdown automaton with 2 stacks. A main stack and an auxiliary stack. The aux stack can not be read or written directly. There are two instructions to interact with the aux stack: aux('a') and main('m'). The aux instruction takes the top element of the main stack and moves it to the top of the aux stack. The main instruction does the same in reverse, move the top element of the aux stack to the main stack.

Name

The name is a wordplay on "basement" and character.

Every instruction in the language is a single character and the language is stack based. The german name for a pushdown automaton (an automaton with a stack) is "Kellerautomat" which can be translated as something like "basement automaton" thus char and basement.

"Proof" why this should be turing complete

A PDA with two Stacks is (or at least should be) turing complete. Generally you can think of the read/write head as being on the top of the main stack. The rest of the main stack is everything that is left from the read/write head, the aux stack is everything that is right from the read/write head. This means an aux instruction is the same as moving left in a turing machine and main is moving right.

Features

Currently this is only a simulation for the above described automaton. Maybe features like arithmetic or logic instructions will be added to make this a stupid compile target. Then there will be a command line flag which turns of the "extra" instructions.

There are some "unnecessary" instructions which could have been implemented using other instructions. For instance the w instruction could have been implemented with aamm. All instructions that currently exist (besides the + instruction) should be things that a normal PDA with access to two stacks should be able to perform.

Examples

There are some examples in the examples directory. For instance the check_anbncn.chase file is can check if an input is of the form a^nb^nc^n which is a context sensitive grammar, thus the automaton can definitely do more than a normal PDA. If this automaton can check every context sensitive grammar obviously can't be tested, but every grammar of the form a^nb^nc^n, a^nb^nc^nd^n... can be checked.

Instructions

TODO add documentation of all instructions

License

This project is licensed under the MIT license see LICENSE for more info.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion by you shall be licensed under the MIT license too.