Migrating from TypeScript

Floe is designed to be familiar to TypeScript developers.

What Stays the Same

• Import/export syntax
• Template literals
• JSX
• Async/await
• Type annotations
• Generics

What Changes

TypeScript	Floe	Example
function	fn	fn greet(name: string) -> string { ... }
: ReturnType	-> ReturnType	fn add(a: number, b: number) -> number
.filter().map()	|> filter |> map	items |> filter(.active) |> map(.name)
let / const	const only	No mutation
===	==	== compiles to ===
switch	match	Exhaustive, no fall-through
try/catch	try expression	const result = try parseYaml(input)
T | null	Option<T>	Some(value) / None
throw	Result<T, E>	Ok(value) / Err(error)

What’s Removed

Feature	Why	Alternative
let / var	Mutation bugs	const only
class	Complex inheritance hierarchies	Functions + records
this	Implicit context bugs	Explicit parameters
any	Type safety escape	unknown + narrowing
null / undefined	Nullable reference bugs	Option<T>
enum	Compiles to runtime objects	Union types
interface	Redundant	type
switch	No exhaustiveness, fall-through	match
for / while	Mutation-heavy	Pipes + map/filter/reduce
throw	Invisible error paths	Result<T, E>
return	Implicit returns	Last expression is the return value

Incremental Adoption

Floe compiles to .ts/.tsx, so you can adopt it file by file. Write new files as .fl, compile them alongside your existing .ts files, and your build tool (Vite, Next.js) treats the output as normal TypeScript.