Rust

Build a Calculator in Rust

Interpreters

Implement an expression evaluator in Rust using postfix notation for calculation.

⏱️ 13h 20min

📦 40 modules

Full Version

What you'll build

We'll build a complete command-line calculator from scratch using Rust. Starting with a minimal REPL, we'll progressively add a tokenizer that breaks expressions into meaningful tokens, implement the Shunting Yard algorithm to convert infix notation to Reverse Polish Notation, and build 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 proper operator precedence, decimal numbers, and clear error messages for invalid input.

Playground Contents

Project Baseline
REPL Greeting
Prompt and Flush
Read Loop With EOF
Blank Lines and Exit Command
Calculator API Stub
Tokenizer Skeleton
Character Iterator
Error Type Foundation
Error Propagation Pipeline
User-Friendly Error Messages
Parenthesis Tokens
Numeric Literal Parsing
Number Validation
Decimal Point Support
Operator Tokens
Shunting Yard Skeleton
RPN Evaluator Stub
Evaluator Error Handling
RPN Test Harness
Number Collection Pass
Parenthesis Grouping
Unmatched Paren Detection
Operator Flushing
Precedence Test Case
Typed Operator Enum
Operator Precedence Logic
Stack-Based Number Evaluation
Paren Guard in Evaluator
Operand Availability Check
Arithmetic Dispatch
Division by Zero Protection
Number Wrapper Type
Centralized Number Parsing
Epsilon-Based Zero Check
Arithmetic Trait Implementations
Unary Minus Detection
Number Parsing Helper
Unary Minus Negation
Unmatched Open Paren Detection

Objectives

Build an interactive REPL with proper I/O handling
Implement a tokenizer for arithmetic expressions
Convert infix notation to RPN using the Shunting Yard algorithm
Evaluate RPN expressions with a stack-based approach
Design a robust error handling pipeline with custom error types
Apply the newtype pattern with trait implementations

Build a Calculator in Rust

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