bytecode.R

# let's construct some byte code
# x <- 42
# y <- x + 42
bcode <- .Internal(mkCode(
  c(
  12L, # this is an identifier which byte-code version you use (I think)
  # each line is an operator, the first item is the operator, followed by operands (aka. arguments)
  16L, 0L, # Operator "LDCONST" (load constant) from the index 1 in the constant pool
  # now value 1 is on the stack
  22L, 1L, # Operator "SETVAR" (set variable) assign the last value on the stack to the name at index 2
  # 1 was removed from the stack, 
  # but the return value of the assignment is now on the stack again
  4L, # let's pop that value,
  20L, 1L, # Operator "GETVAR": let's load x (get var operator)
  # since 1 is now on the stack, we need to add 1 to it and then assign it
  # to y
  16L, 0L, # Now let's load a constant again from index 1
  44L, 2L, # Let's add the last two values. Add has one argument, the original expression. Not sure why
  22L, 3L, # now set the value on the stack to the name at index 4
  15L, # make the value in visible
  1L # return
  ),
  list(# the constant pool (a list of values and some rules)
    42,
    as.name("x"),
    quote(x + 42),
    as.name("y")
  )
))
print(eval(bcode))
#> [1] 84
print(x)
#> [1] 42
print(y)
#> [1] 84