Everyday VCL #

This chapter mirrors TS Handbook “Everyday Types,” but in VCL’s indent-first, dot-terminated style.

Blocks, indentation, trailing dots #

• Indentation defines scope; tabs are disallowed. Use spaces consistently.
• Statements end with a trailing dot (.). Missing dots are a common error.
• Example:

define greet.
  let message = "hi".
  log message.

Values and literals #

• Primitives: number, string, boolean, none.
• Records: { name: "ada", age: 36 } (keys are identifiers; strings allowed via quotes).
• Variants (sum types): Ok(value) / Err(reason) pattern; pattern matching is planned—today treat as tagged data.
• Arrays: [1, 2, 3].

Bindings #

• let introduces a binding in the current scope.
• Reassignment is allowed with let x = ... again in the same scope; shadowing is permitted in nested scopes.

Control flow #

• when <condition>. introduces a block. Use else. for alternate branch.

when user.is_admin.
  log "admin".
else.
  log "user".

• ensure / validate / expect are semantic checks (see Effects chapter for failure semantics).

Functions / handlers #

• Define named handlers with define name.. Handlers take a single implicit ctx record; additional params are pattern fields inside ctx (common convention). Example:

define add_user.
  let { name, email } = ctx.
  store { path: "users", value: { name, email } }.
  return { status: "ok" }.

Types (lightweight) #

• VCL is structurally typed; most code is inferred. Explicit type annotations are currently minimal; use the spec for edge cases.
• Truthiness: only none is falsy.

Common pitfalls #

• Missing trailing dots.
• Mixed tabs/spaces in indent.
• Forgetting to return a value from handlers that the runtime expects.

See also: Language Spec for formal grammar and Stdlib for available helpers.