Function insertBefore

insertBefore(
    program: Program,
    index: number,
    instructions: Instruction[],
): Program
Inserts instructions before a position.
Parameters
- program: Program
  Program to edit.
- index: number
  Position to insert before. Past the end appends instead.
- instructions: Instruction[]
  Instructions to insert.
Returns Program
A new program; the input is left untouched.