Session 5 homework

[maw3193]

Continuing the bft project, this time we're making the interpreter do things!

• [x] Task Zero - things I missed
  • [x] I don't need to store the index to a particular instruction if I'm also storing a copy of that instruction (and they're unique), I can binary_search the Vec for it.
• [x] Task One - Shaking your head
  • [x] Add a member to the interpreter struct to represent the head location. Default location is 0.
  • [x] Create an enum of interpreter errors (VMError), the error should include the offending instruction. Known error cases:
  • [x] Seek to below zero
  • [x] Seek beyond the end and auto-extend is not enabled
  • [x] Include a borrow of the Program inside the Interpreter
  • [x] Make sure tests are updated
  • [x] Update main
  • [x] Remove vestigial "interpret" functions
  • [x] Add methods to move head left or right (&mut self), return a Result because they could cause VMError.
  • [x] Document and test success and failure.
• [x] Task Two - Traits and maths
  • [x] Add a new trait called CellKind which has the same constraints as used to implement new().
  • [x] Rewrite the old impl block to use CellKind.
  • [x] Add methods to increment/decrement to the CellKind trait.
  • [x] Test with impl CellKind for u8
  • [x] Add any other tests/docs to ensure this is usable.
• [x] Task Three - Basic I/O
  • [x] Give the CellKind trait a set_value() method that takes a u8.
  • [x] Extend VMError with IOError, this error takes the underlying IO Error and the offending instruction.
  • [x] interpreter method read_value() reads a byte from stdin (note: brainfuck is always bytes, even if larger values can be stored in cells)
  • [ ] Add a From impl to convert from std::io::Error to VMError. This might be tricky, the important part is being able to use the ? operator on anything that returns a Result<_,VMError>.
  • [x] Interpreter method to output bytes which takes a Write impl.
  • [x] Similarly to read, we need a CellKind method to retrieve a byte from a cell and wrap up IOErrors.
  • [x] Document and test. Use std::io::Cursor<Vec<u8>> to get around need for stdin and stdout.
• [ ] Task Four - Thinking Ahead
  • We've done seeking, we have methods for incrementing/decrementing the value at the pointer, and we've got read/write. Have a think about how to implement the [ and ] instructions.
  • [ ] Have another look over docs, examples and tests with an eye to usability.

[maw3193]

It might be more convenient for me to also implement a DecoratedProgram::from_file, but that'll need some more thought, because it could have an IOError, or a ParseError.

[maw3193]

I think I've avoided needing to write a From impl for converting from a std::io::Error to a VMError, this might be because thiserror can automatically implement From when an error's Source is specified.