Example implementation of LC3

[JulianGCalderon]

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This PRs adds an example implementation of a LC3 virtual machine, based on Write your Own Virtual Machine, by Justin Meiners and Ryan Pendleton.

I added the full implementation to examples/lc3. Additionally, I changed some elements of the standard library.

The implementation contains some FIX notes, that indicate that I had to use a hacky solution to workaround a current limitation of the language.

Some important features that are missing are:

• Call a method from inside of a method
• Take references of struct indexes or array elements: &self.field.inner or &self.field[3].
  • This allows for calling method on struct field elements.
• If-Else chains.
• Match statement for non enum values.
• C-like Enums?
• Initializing static arrays without specifying every value: [0; 3] instead of [0, 0, 0].
• Bitwise operations: &, <<, >>.

Debugging is also bit difficult right now, as we don't have a good way to format values. The workaround I found is to write raw data to a file, and read it with another tool. As an example, I added a justfile with some commands that allowed me to inspect the raw data.

Implementation

• [ ] Inst: BR
• [x] Inst: ADD
• [ ] Inst: LD
• [ ] Inst: ST
• [ ] Inst: JSR
• [x] Inst: AND
• [ ] Inst: LDR
• [ ] Inst: STR
• [ ] Inst: RTI
• [ ] Inst: NOT
• [ ] Inst: LDI
• [ ] Inst: STI
• [ ] Inst: JMP
• [ ] Inst: RES
• [x] Inst: LEA
• [ ] Inst: TRA
  • [ ] Trap: GETC
  • [x] Trap: OUT
  • [x] Trap: PUTS
  • [ ] Trap: IN
  • [ ] Trap: PUTSP
  • [x] Trap: HALT