The Substitution Model of Evaluation

We need to build a mental model of how Scala expressions are evaluated so we can understand what our programs are doing. We've been getting by with an informal model so far. In this section we make our model a bit more formal by learning about the substitution model of evaluation. Like many things in programming we're using some fancy words for a simple concept. In this case you've probably already learned about substitution in high school algebra, and we're just taking those ideas into a new context.

import cats.effect.unsafe.implicits.global
import doodle.core.*
import doodle.image.*
import doodle.syntax.all.*
import doodle.image.syntax.all.*
import doodle.java2d.*