Kaguya

Kaguya is an implementation of Brainf**k by Ruby.

This implementation consits of following elements,

• Tiny parser
• Tiny compiler
• Tiny virtual stack machine

Installation

$ gem install kaguya

Usage

$ kaguya helloworld.bf

An option --debug helps you to see AST and instruction sequence.

$ kaguya --debug helloworld.bf

Technical components

Parser

https://github.com/mozamimy/kaguya/blob/master/lib/kaguya/parser.rb

The parser parses a BF script one charactor at a time. Errors can be raised by the parser if the script contains invalid corresponding of [ and ] or invalid charactors.

Only the root node and while nodes have children.

Virtual machine

https://github.com/mozamimy/kaguya/blob/master/lib/kaguya/vm.rb

Kaguya VM has a two stacks (left_stack, right_stack) and has following 9 instructions,

• forward: Forward stack, if right_stack is empty then push 0 to left_stack else move top of right_stack to left_stack.
• backward: Backward stack, top data of left_stack is poped and pushed to right_stack.
• increment: Increment top of left_stack.
• decrement: Decrement top of left_stack.
• output: Output top of left_stack to standard I/O.
• input: Input a value from standard I/O and push it to left_stack.
• branch_ifzero N: Jump to an instruction at PC - N if top of left_stack is 0.
• branch_unlesszero N: Jump to an instruction at PC - N unless top of left_stack is 0.
• leave: Exit

Compiler

https://github.com/mozamimy/kaguya/blob/master/lib/kaguya/compiler.rb

Kaguya compiler compiles an AST generated by the parser to an instruction sequence for Kaguya VM.

Example

[20:17:51]mozamimy@queen:kaguya (master) (-'x'-).oO(
> cat example/useless.bf
>>+[<>[+-]]
[20:17:53]mozamimy@queen:kaguya (master) (-'x'-).oO(
> be exe/kaguya --debug example/useless.bf
=== AST ===
#<Kaguya::AST::Node:0x007fd755a3f8c0
 @children=
  [#<Kaguya::AST::Node:0x007fd755a3f780
    @children=[],
    @parent=#<Kaguya::AST::Node:0x007fd755a3f8c0 ...>,
    @type=:forward>,
   #<Kaguya::AST::Node:0x007fd755a3f500
    @children=[],
    @parent=#<Kaguya::AST::Node:0x007fd755a3f8c0 ...>,
    @type=:forward>,
   #<Kaguya::AST::Node:0x007fd755a3f230
    @children=[],
    @parent=#<Kaguya::AST::Node:0x007fd755a3f8c0 ...>,
    @type=:increment>,
   #<Kaguya::AST::Node:0x007fd755a3f028
    @children=
     [#<Kaguya::AST::Node:0x007fd755a3edd0
       @children=[],
       @parent=#<Kaguya::AST::Node:0x007fd755a3f028 ...>,
       @type=:backward>,
      #<Kaguya::AST::Node:0x007fd755a3e7e0
       @children=[],
       @parent=#<Kaguya::AST::Node:0x007fd755a3f028 ...>,
       @type=:forward>,
      #<Kaguya::AST::Node:0x007fd755a3e5b0
       @children=
        [#<Kaguya::AST::Node:0x007fd755a3e3f8
          @children=[],
          @parent=#<Kaguya::AST::Node:0x007fd755a3e5b0 ...>,
          @type=:increment>,
         #<Kaguya::AST::Node:0x007fd755a3e1f0
          @children=[],
          @parent=#<Kaguya::AST::Node:0x007fd755a3e5b0 ...>,
          @type=:decrement>],
       @parent=#<Kaguya::AST::Node:0x007fd755a3f028 ...>,
       @type=:while>],
    @parent=#<Kaguya::AST::Node:0x007fd755a3f8c0 ...>,
    @type=:while>],
 @parent=nil,
 @type=:root>
=== ISEQ ===
[[:forward, nil],
 [:forward, nil],
 [:increment, nil],
 [:branch_ifzero, 8],
 [:backward, nil],
 [:forward, nil],
 [:branch_ifzero, 4],
 [:increment, nil],
 [:decrement, nil],
 [:branch_unlesszero, -2],
 [:branch_unlesszero, -6],
 [:leave, nil]]
=== RUN ===

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/mozamimy/kaguya.

License

The gem is available as open source under the terms of the MIT License.