Why is it called "typed errors"?

The feature behind either has famous names in other ecosystems — Monad, Railway-oriented programming. This page explains why FxDart deliberately calls it none of those. (Never met a monad? Start with Monad & comprehension blocks.)

Why not "Monad"?

Because it would misdescribe the feature. The whole point of the Raise design is that it is not monadic style — it exists to replace flatMap-chaining with straight-line code. You saw this on the typed errors page: the either((r) { ... }) block is the alternative to the nested flatMap pyramid, not a wrapper around it.

Kotlin's Arrow — the design source for this feature — went through exactly this decision. Arrow 1.x had a Monad typeclass, higher-kinded-type emulation, and the Haskell vocabulary to go with it. Arrow 2.x deleted all of it, and even renamed the core operation shift → raise by community poll — choosing the word users understood over the word theory used. The lesson generalises: name for the audience you want, and FxDart's audience is ordinary Dart developers, not category theorists.

There is also a cautionary tale in Dart itself: FP libraries whose public surface speaks Haskell (Monad2, HKT, Do-notation) intimidate exactly the developers who would benefit most from typed errors. A page called "Monad" would scare off its own readers — and describe the one thing this API isn't.

Why "typed errors"?

It says what the feature does — errors carried in the type system instead of thrown past it — rather than what category theory calls the shape.
It is Arrow's own name. The corresponding chapter of the Arrow documentation is literally titled Typed errors, so Kotlin developers searching for the Dart equivalent land on the right words.
It follows the house rule. FxDart's naming philosophy (see WHY_CURRIED.md: "port the meaning, not the spelling") is: Dart names, not Haskell names — map not fmap, flatMap not bind-the-verb, recover not handleErrorWith.

Why not "raise"?

raise is the accurate "cool" name — it is what the DSL is actually called, and tutorial URLs here are function-named (concurrent.html, fx.html). It was reserved on purpose: if Section 13 later gains per-function tutorial pages (either.html, bind.html, …), a raise.html overview would collide with the future raise function tutorial. typedErrors.html stays free as the section's overview page forever.

What about "Railway"?

Railway-oriented programming is a well-known metaphor for the same idea (a success track and a failure track). It is a fine mental model — and a poor page name: less searchable, not Arrow vocabulary, and a metaphor you must already know before it helps you.

The principle in one line. A name is part of the API: it should tell a Dart developer what the thing does, in words they would search for — typed errors — not certify which abstraction it secretly is.