Types and why you should care

Typed vs Untyped

Typed

Untyped

Fortran

C

C++

Java

Swift

Rust

OCaml

Haskell

Lisp

Python

JavaScript

Ruby

Lua

Clojure

Racket

Some vocabulary

• Value
• Variable
• Expression
• Type

Typed vs Untyped

• untyped: values have types
• typed: variables and expressions have types

Why Types?

• Make programs faster
• Make programs easier to reason about

How do types hurt?

• Increase verbosity
• Cause confusion
• Slow you down
• Interfere with your plan

How can types help?

• Improve performance
• Detect errors
• Communicate your intent
• Inform your tools
• Guide refactoring
• Enforce invariants

Things to remember

• Don't judge types by their worst face
• Don't forget the tradeoffs
• Learn more languages!