Exercise: Rewriting with Result

In this exercise we're revisiting the expression evaluator exercise that we did in day 2. Our initial solution ignores a possible error case: Dividing by zero! Rewrite eval to instead use idiomatic error handling to handle this error case and return an error when it occurs. We provide a simple DivideByZeroError type to use as the error type for eval.

# // Copyright 2023 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
{{#include exercise.rs:types}}

{{#include exercise.rs:eval}}

{{#include exercise.rs:tests}}

• The starting code here isn't exactly the same as the previous exercise's solution: We've added in an explicit panic to show students where the error case is. Point this out if students get confused.