Bytecode VM

Implement a stack-based virtual machine that executes compiler bytecode.

Function signature

func Run(bc Bytecode) (Value, error)

Bytecode types

Use the provided types:

• Bytecode with Main []Instr and Functions []Function
• Function with Name, Params, and Code []Instr
• Instr with Op, Int, and Str

Value types

Use the provided Value struct with kinds:

• number
• string
• bool
• nil

Runtime rules

Truthiness

• false and nil are falsey
• everything else is truthy

Arithmetic / comparison

• + - * / work on numbers
• + also supports string concatenation when both operands are strings
• < <= > >= work on numbers
• == / != compare by type and value

Type mismatches should return a non-nil error.

Variables and scopes

• DEFINE_VAR / DEFINE_CONST create bindings in the current scope
• STORE updates the nearest existing binding (error if const)
• LOAD reads the nearest existing binding
• ENTER_SCOPE / EXIT_SCOPE push and pop scope maps

Functions

• Functions are stored in Bytecode.Functions and called by name (CALL).
• Create a new local scope for each call, bind parameters, then execute the function body.
• If a function returns without RETURN, its result is nil.
• Functions can read global variables but we do not implement closures.

Program result

After executing Main, return the top of the stack if present; otherwise return nil.

Notes

• Use absolute jump targets.
• Keep the VM readable and straightforward.