Known Limitations

What Echo still does not do. As of 0.8.9, the language includes modules, CLI tooling, first-class functions, const / destructuring / unions / switch, and nominal classes with new { ... } fields (including defaults), bound/unbound/type methods, optional implements, and interfaces (no inheritance). This page is the remainder — not a changelog.

Already in (summary)

• Core syntax and v0.3 file modules (import / export)
• Host/stdlib, REPL, check / test / fmt / lint
• 0.6–0.7: lambdas, collection helpers, const, destructuring, exact objects, unions, switch, range-as-value
• 0.8: class + new { ... }, methods + this, unbound/type methods, interface, optional implements

Details: Roadmap and CHANGELOG.md.

Current Limitations

• No class inheritance (extends); shared behavior is interfaces + composition
• Compound assignment (+= / -= / *= / /= / %=) works on simple names only — not on member fields (this.x += 1 is not supported yet; use this.x = this.x + 1). Planned for the next version after 0.8.9
• No generics
• No exceptions such as try/catch — abort stays the default; recovery is inquiry and *Or twins (failure model). echo test may continue after expect* failures; that is runner-only, not in-language recovery
• No overloads
• Function scope is lexical; reassignment of outer variables still requires use mut
• Nested collections inside a frozen list/hash are not recursively frozen; a nested value reached through a different mutable name can still be mutated
• Open object type aliases accept extra fields; use exact { ... } to reject them
• Union types do not narrow in if type(x) == "..."; use switch type arms. null is not a type — use str | void when needed
• Hash runtime indexing only supports string keys
• clone() is shallow
• format() only supports positional placeholders
• Interpolation tokenization is not fully strict
• No mkdir -p or recursive delete
• No dates, HTTP, or regex builtins
• No LSP (the editor extension runs CLI tasks into the Problems panel; that is not a language server)

Why this page exists

So docs do not oversell the language, and so shipped work is not mistaken for missing.

Where next work is tracked

See Failure model, Roadmap, and priority.