return.c

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/*
 * This file is part of the Fun programming language.
 * https://fun-lang.xyz/
 *
 * Copyright 2025 Johannes Findeisen <you@hanez.org>
 * Licensed under the terms of the Apache-2.0 license.
 * https://opensource.org/license/apache-2-0
 */
 
/**
 * @file return.c
 * @brief Implements the OP_RETURN opcode for returning from a function in the VM.
 *
 * This file handles the OP_RETURN instruction, which returns from the current function
 * and optionally pushes a return value onto the stack.
 *
 * Behavior:
 * - Pops the optional return value from the stack.
 * - Returns to the caller frame.
 * - Pushes the return value onto the stack (if any).
 *
 * Error Handling:
 * - Exits with an error if the frame stack is empty.
 *
 * Example:
 * - Bytecode: OP_RETURN
 * - Stack before: [42]
 * - Stack after: [42]
 */
 
case OP_RETURN: {
  Value retv;
  if (vm->sp >= 0)
    retv = pop_value(vm);
  else
    retv = make_nil();
  vm_pop_frame(vm);
  push_value(vm, retv);
  break;
}