Known Limitations

Not a beginner lesson

This page lists what Echo does not do yet, plus a historical feature timeline. For learning, use Learn Echo. Current package version: 2.2.1.

What Echo still does not do. As of 2.2.1, the language includes modules (sibling + nested / relative paths, std/… install-tree imports through std/re / std/time / std/yaml / std/math / std/random, optional --require-std prelude policy, clearer cycle / not-found diagnostics), CLI tooling (check / test / fmt / lint / builtins / std / lsp / ide), first-class functions, const / destructuring / unions / switch, nominal classes with new { ... } fields (including defaults), bound/unbound/type methods, optional implements, interfaces (no inheritance), compound assignment on members, priv visibility, positional construction, deep clone(), named format placeholders, class properties (get / set), recursive mkdirAll / removeTree, regex builtins (also std/re), union narrowing in if type(...), thin UTC dates (also std/time), thin HTTP (also std/http), thin URL helpers (also std/url), Base64 helpers (also std/base64), YAML helpers (yamlParse / yamlParseOr / yamlWrite, also std/yaml, E2855), file/JSON/env helpers also via std/fs / std/json / std/os, math / random / now / wait / run also via std modules, watch location / abort dumps, abort Stack: dumps and trace, documented E2801 / E2850–E2855 and module E3001–E3005 codes, playground host-policy docs plus playground std/… / YAML demos, a thin elang lsp stub wired into the editor extension (diagnostics, builtin hover, goto-def; task matchers remain as fallback), and generated builtin + std inventories (tools/sync_builtins.py). 2.0 is path resolution + std modules — not a package registry. 2.1 is YAML + LSP stub + std maturity on that surface. This page is the remainder — not a changelog.

Already in (summary)

• Core syntax and file modules (import / export; nested / relative paths in 2.0.0; std/… in 2.0.2)
• 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
• 0.9.0: compound assignment on class fields (this.x += 1)
• 0.9.1: priv on fields and methods (class-private)
• 0.9.2: positional construction Point(3, 4) (named Point { ... } still works)
• 0.9.3: deep clone() for lists, hashes, and class instances
• 0.9.4: named format() placeholders via trailing hash
• 0.9.5: class properties get / set (soft keywords; field-style access)
• 0.9.6: mkdirAll(path) / removeTree(path) for recursive create/delete
• 0.9.7: regexMatch / regexFind / regexReplace / regexSplit (Python re)
• 0.9.8: union narrowing in if type(x) == "..." (and matching else if)
• 0.9.9: formatTime / parseTime (UTC) plus days / hours / minutes
• 1.0.0: stable release (same surface as 0.9.9)
• 1.1.0: httpGet / httpPost with Host.allow_http
• 1.1.1: request headers, httpOk / httpRedirect, httpGetOr / httpPostOr
• 1.1.2: urlEncode / urlDecode / urlJoin / urlQuery
• 1.1.3: watch source locations + Watched: dump on abort
• 1.1.4: error-message / code pass (E2801, E2850–E2853 documented)
• 1.1.5: playground host-policy docs (CLI vs playground Host)
• 1.1.6: tools/sync_builtins.py + builtin inventory page
• 1.1.7: base64Encode / base64Decode (E2854)
• 1.1.8: elang builtins (+ -V / help epilog)
• 1.1.9: series close (README / examples / playground docs for full 1.1 surface)
• 2.0.0: relative / nested import paths ("./math", "lib/math", "../shared")
• 2.0.1: clearer E3001–E3003 diagnostics (looked-for path, import location, nested cycle labels)
• 2.0.2: import … from "std/…" from the Echo install tree (seed std/meta)
• 2.0.3: HTTP family via std/http (prelude names still work)
• 2.0.4: URL + Base64 via std/url / std/base64 (prelude dual-path)
• 2.0.5: files / JSON / env via std/fs / std/json / std/os (prelude dual-path)
• 2.0.6: regex + dates via std/re / std/time (prelude dual-path)
• 2.0.7: optional --require-std / Host.require_std (core vs peeled prelude)
• 2.0.8: docs / examples / playground for multi-file + std/…
• 2.0.9: 2.0.x series close (path resolution + std modules, not a package manager)
• 2.1.0: yamlParse / yamlWrite (E2855); std/yaml
• 2.1.1: yamlParseOr + failure-model / docs
• 2.1.2: elang lsp thin stdio stub (diagnostics + builtin hover)
• 2.1.3: LSP goto-def for local + imported symbols
• 2.1.4: editor LSP client (elang lsp via vscode-languageclient; task matchers remain)
• 2.1.5: abort Stack: dump + trace helper (no stepper)
• 2.1.6: further std peel (std/math, std/random; now / wait on std/time; run on std/os)
• 2.1.7: elang std lists install-tree std/… modules (--exports / --count / --path)
• 2.1.8: generated Std Inventory docs page (tools/sync_builtins.py)
• 2.1.9: 2.1.x series close (YAML + LSP stub + std maturity on 2.0 modules)
• 2.2.0: elang ide desktop editor (Tk window: edit → Run → output, line numbers, syntax highlight)
• 2.2.1: crash hardening + path safety (oversized ints / recursion / symlink + removeTree guards; fmt / switch unescaping)

Details: Roadmap and CHANGELOG.md.

Current Limitations

• No class inheritance (extends); shared behavior is interfaces + composition
• No generics
• No exceptions such as try/catch — abort stays the default; recovery is inquiry and *Or twins (failure model). elang 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
• null is not a type — use str | void when a binding may hold null. Full flow-sensitive typing beyond simple-name if type(...) guards is not implemented
• Hash runtime indexing only supports string keys
• format() has no width / precision / alignment specs
• Properties are not part of interfaces (implements still checks methods only)
• Interpolation tokenization is not fully strict
• No date object type / local-timezone calendars (UTC unix seconds + formatTime / parseTime only)
• HTTP is thin (no cookies/session client, no multipart); playground denies HTTP (allow_http=False)
• No full LSP-as-product (thin elang lsp + editor client ship in 2.1.2–2.1.4; tasks/matchers remain)
• elang ide is an MVP desktop editor (edit / Run / output, Open/Save, syntax highlight) — no autocomplete, no debugger, no project tree, no LSP inside the window; interactive ask / readLine are limited (non-interactive programs are the happy path)
• No full debugger / stepper (abort Stack: + watch + trace ship through 2.1.5)
• No package registry yet (stdlib peels + optional --require-std shipped through 2.0.7)

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.