How does one do Codeable/Programmable Magic

If possible, how does one make a Codeable/Programmable Magic like Psi, Ars Nouveau, and Thaumcraft?

For example: 

• A spell that spawns a life stealing projectile that homes in to a mob
• A spell that does an AoE attack to only certain types of mobs
• A spell that creates a platform that disappears in a couple seconds

(I don't know if this is fit for this forum section)