Calculator in Rust

What you'll build

We'll build a fully functional command-line calculator from the ground up in Rust. Starting with a minimal REPL, we progressively add a tokenizer that splits expressions into meaningful tokens, implement the Shunting Yard algorithm to convert infix notation into Reverse Polish Notation, and assemble a stack-based evaluator that computes the final result.

Along the way we'll practice idiomatic Rust patterns: custom error types with Display, the Result/? pipeline, newtype wrappers, trait implementations (FromStr, Add, Sub, Mul, Div), and test-driven development. By the end, our calculator handles parenthesized expressions with correct operator precedence, decimal numbers, and clear error messages for invalid input.

Learning objectives

✓Build an interactive REPL with clean input/output handling

✓Implement a tokenizer for arithmetic expressions

✓Convert infix notation to RPN using the Shunting Yard algorithm

✓Evaluate RPN expressions with a stack

✓Design a robust error-handling pipeline with custom error types

✓Apply the newtype pattern together with trait implementations

Prerequisites

▸Basic Rust syntax (functions, enums, structs)

▸Familiarity with pattern matching and the Result type

▸Understanding of basic arithmetic and operator precedence

Course curriculum

1 Interactive shell

—Project skeleton

—Read loop

—Shell commands

2 The calculate function and the tokenizer

—Entry point

—The tokenizer skeleton

—The CalcError error type

3 Parsing numbers

—The number collector

—Tests and fractional numbers

4 Tokens

—The Token type

—Tokenization test

5 Operators

—The operator token

—The Operator type

—The unary minus

6 Parentheses

—Parenthesis tokens

—Tracking context

7 Shunting yard

—The to_rpn skeleton

—Operator precedence

—Closing parentheses

—Final parenthesis checks

8 Stack-based evaluation

—The eval_rpn skeleton

—Operations on the stack

—Evaluation errors

—Unary minus in the evaluator

Technologies

Rust Calculator Shunting Yard Reverse Polish Notation Tokenizer REPL Error Handling Newtype Pattern

FAQ

Is this a video course?

No. You work through the project step by step in your browser, and the reference code for each step saves to your disk — yours to run and keep locally.

Do I need to install anything?

No. The playground runs entirely in your browser — no toolchain or local setup required.

Can I try it before subscribing?

Yes. Preview steps are available without a subscription so you can see the format and quality first.

What do I get with full access?

Every step unlocked, the Workbench app, a snapshot for each step, jump-to-any-step navigation, and all new playground releases.

Does it work with an AI agent like Claude or Codex?

Yes. You can work through a playground solo or alongside an AI agent.

Is there reference code?

Yes. Every step has a complete reference solution you can compare against.