Tagged template sin función de tag correspondiente

Why this fires¶

A tagged template tag"…" is not special syntax — the compiler lowers it to an ordinary function call:

sh"git log -n {n} --oneline"
// ⇒ sh({"git log -n ", " --oneline"}, n)

So the tag must resolve to a function in scope (a local, a top-level fn, a prelude builtin like sh, or a plugin-exported function like ts). When it resolves to nothing anywhere, the call could only fail at runtime with attempt to call nil — TE970 surfaces the problem at check time instead, usually catching a typo in the tag name:

let out = hs"git status".run()?
//        ^ error[TE970]: tagged template `hs"…"` has no matching
//          function `hs` in scope. Did you mean `sh"…"`?

Fix it¶

1. Fix the typo¶

The diagnostic suggests the nearest name in scope (edit distance):

let out = sh"git status".run()?   // `sh` is a prelude builtin

2. Define (or import) the tag function¶

Any function with the shape fn tag(parts: [str], args: ...Any) -> T can be a tag. The literal chunks arrive in parts; each interpolated value arrives as its own argument — already separated, which is what makes tags injection-safe by construction:

fn upper(parts: [str], args: ...Any) -> str {
    // interleave parts and args, uppercasing the literals …
}

let s = upper"hello {name}"

Notes¶

• sql"…" and json"…" never fire TE970 — they have bespoke compile-time lowering and validators instead of a runtime tag function.
• Plugin tags (ts"…", js"…", …) are resolved through the plugin registry at runtime; any tag matching a function exported by a bundled plugin declaration is left permissive.
• When the tag resolves to a function with a known return type, the template is typed as that return type (e.g. sh"…" types as Cmd), so chained calls like .run()? check properly.

See also¶

• TE100 — undefined variable (same resolution rules).
• specs/shell-scripting.html §1 — command literals over tagged templates.