day5-1.prdc

iIgHr{\H=b|}—G{•)+vHt}—T{\ABD0+3T)Gzu\a~Hu4}—O0λ·H=1h‰9%[E_Š_ObÞ_Ob{1T~Ho2}{1T~G:P_&2}]=~•+} .. 92 bytes

{
i   .. read full input
Ig  .. read int groups thereof
Hr  .. put this array into H, the default hoard

.. helper function Get: mode value digit, value -> value or indexed value
{\H=b|}—G
.. helper function Translate: given x, get values of next x arguments
{•)+vHt}—T

.. helper function BinaryOperator
.. parameter mode value, function -> do it and leave a pc increment
{
  \      .. swap operator, deal with it later
  ABD    .. reversed digits of parameter mode value
  0+     .. with a 0 on the end to ensure at least two elements
  3T)    .. get three argumnets; uncons the last
  Gzu    .. zip with helper Get under the last; stack: operator, source_operands, dest_address
  \a     .. swap around the middle. stack: dest_address, source_operands, operator
  ~      .. apply
  Hu     .. update H
  4      .. leave 4, indicating to increment pc by 4
}—O

0   .. pc
λ   .. infinite loop
  ·   .. assign pc to bullet
  H=  .. index pc into H to get the "first value" of an instruction
  1h‰ .. divmod 100 to get the parameter mode value and the opcode
  9%
  [
    E_
    Š_Ob .. sum
    Þ_Ob .. product
    { .. input
      .. ;      .. pop the parameter mode value, not needed
      .. we can actually leave junk on the stack since we explicitly terminate
      1T~    .. get 1 arg
      Ho     .. update 1 where specified
      2 .. increment pc by 2
    }
    { .. output
      1T~G   .. find argument, index again if imode
      :      .. duplicate;
        P_   .. print...
      &      .. if true
      .. (if false we'll leave it on the stack, but no harm)
      2 .. increment pc by 2
    }
  ]=~
  •+ .. leave new pc on stack
}
};