████  blue          nord7 → nord8 → nord9 → nord10
────────────────────    teal   cyan   light  deep blue
a Ruby/Elixir surface on tatara-lisp and Rust

blue is the pleme-io language. A Ruby/Elixir surface parses to a tatara-lisp AST, macros are term rewriting on that AST, and the runtime is Rust — not the BEAM.

The mark is a blueshift

Four solid cells walking Nord's Frost band toward blue. Blueshift is blue's central metaphor — the wave that shifts with you across tatara-lisp and Rust as you write — and a blueshift is a shift in colour, so the mark shifts colour.

Named by ANSI slot, never by hex, so it renders in your Nord and follows you if you retheme.

Declare nothing and blue is dynamic and fast. Annotate one function and that function gets analysis. Nothing else changes — same tree, same answer, same speed.

def add(a, b)                      # no annotation, no analysis
  a + b
end

def fact(n: Int) -> Int            # annotated — this one is checked
  if n < 2
    1
  else
    n * fact(n - 1)
  end
end

blue check prints what that cost, so the claim is a measurement rather than a promise:

$ blue check example.b
typed declarations: 1
nodes analysed:     11
seams:              0

Try it

nix run github:pleme-io/blue -- run example.b

Command
blue run FILE	parse, type-check, erase, execute
blue test FILE	run the file's test blocks
blue fmt FILE [--check|--write]	the one formatting
blue check FILE	what the type checker did
blue ast FILE / blue erase FILE	the tree with and without annotations — the sliding scale, visible
blue deps FILE / blue posture FILE	read a Bluefile
blue lsp	language server over stdio
blue banner	the wordmark

What is here

Macros with bounded expansion — a runaway macro is a typed error naming the macro, not a dead compiler. OTP-style supervision with private per-process environments and copy-on-send. A test framework whose failures print the expression as blue source. A package manager whose manifest is itself a blue program. A WASM target that runs the whole language in an engine with zero host imports.

$ blue test spec/macros.b
FAIL a macro expands
  assert double(21) == 43
3 test(s): 2 passed, 1 failed

The failure message is the formatter's output, so it reads exactly as written.

What is not

Stated plainly, because a language's honest gaps matter more than its claims:

• No per-process GC heap. Processes have private environments and messages are deep-copied, but reclamation is Arc refcounting — there is no independent per-process collection pause.
• Not self-hosted. The toolchain is Rust. spec/*.b is blue specifying blue, which is the specification axis only.
• Nothing fetches. Dependency resolution is real; there is no registry client.
• The formatter refuses a comment it cannot place. Comments before or after a top-level form are preserved; one buried inside an expression is refused rather than dropped, because those lines get re-laid out.

The full tier ledger — every row marked SHIPPED or ABSENT — is theory/BLUE.md §V.26.

Theming

Colours come from irodori, the fleet's Nord palette. blue carries no hex of its own: nord10 (#5E81AC, deep frost blue) is its identity, and nord8 frost-cyan stays the fleet's shared interaction colour — identity and interaction are different roles.

Building

nix build .#blue          # hermetic
cargo test --workspace    # 306 tests

MIT.