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# Buttons the Computer
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This is a simple demo project for the [Learn JS the Hard Way Course](https://learnjsthehardway.com)
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and also the implementation of the first module introducing the concept of a Turing Machine. In the
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beginning of the course I'll be introducing a very simple little computer that is a functional
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Turing Machine, although not something you'd actually want to use. It's purpose is to show how
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basic computation works, and to provide a simple assembly language anyone can understand. It also
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provides a simply UI that you can code the computer by only clicking on buttons.
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This project was implemented in one day on a Saturday while playing Diablo III on breaks. If you
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find bugs awesome, let me know. I'll most likely find more as I work on it, but don't expect this
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to be a billion dollar project.
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# The Machine
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Buttons is a simple stack machine with arbitrary registers and a limited amount of power known as
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"ticks" of which you have 128. What does that mean in practice?
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1. You do most of your calculations by working a stack with PUSH and POP.
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2. You can store things in a register and name that register anything you want.
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3. Every operation takes 1 tick to process.
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4. You have only 128 ticks to complete your calculation.
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5. You can do all of this with only a single mouse with two buttons.
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6. The data type for the stack is whatever JavaScript does with numbers.
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# Operations
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The current operations are:
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* ADD - Add the two numbers on the top of the stack, replace them with the result.
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* SUB - Subtract just like add.
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* DIV - Divide just like add.
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* MUL - Multiply just like add.
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* MOD - Modulus just like add.
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* POP - Take the top of the stack off and throw it away.
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* PUSH - Push a new value onto the stack.
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* HALT - Stop the computer with a message, probably an error.
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* JUMP - Jump to a line number. Lines start at 0.
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* JZ - JUMP but only if the top of the stack is 0.
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* JNZ - JUMP but only if the top of the stack IS NOT 0.
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* CLR - Clear the machine, kind of a soft reset, good for debugging in a loop.
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* STOR - Take the top of the stack and assign it to a register by a name.
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* RSTOR - Take the named register and push it onto the stack.
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# Samples
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You can try these example programs out at [buttons.computer](https://buttons.computer):
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```asm
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PUSH 1
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PUSH 2
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ADD
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```
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```asm
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PUSH 1
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PUSH 1
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ADD
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JUMP 1
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```
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```
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PUSH 20
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PUSH 1
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SUB
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JZ 5
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JUMP 1
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```
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```
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PUSH -20
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PUSH 1
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ADD
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JNZ 5
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JUMP 1
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```
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```
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PUSH 100
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STOR AX
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PUSH 50
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ADD
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RSTOR AX
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SUB
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```
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```
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PUSH 0
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STOR AX
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RSTOR BAD NAME
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PUSH 100
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ADD
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```
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# License
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This software is fully Copyright (C) Zed A. Shaw 2020. It's like a painting at a museum. You can
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look at it and admire its beauty, but you don't own it and can't take it home with you.
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