Symbols

A symbol is an identifier-like value written :name — no space between the colon and the name. Symbols are used for tags, enum-like choices, and any time you want a typed name rather than a string.

shade  = :amber
accent = :cyan
edge   = :uses

The symbol type

A free-form field accepting any symbol has type symbol. There's no validation on which symbols may appear — anything that lexes as :name is valid.

type Tag {
  name: utf8
  kind: symbol
}

t = Tag { name: "release", kind: :stable }

Symbol sets

A symbol_set names a closed vocabulary of symbols. A field typed by the symbol set is restricted to exactly those members, giving you an enum-like type without the weight of a union.

symbol_set Color {
  red
  green
  blue
}

type Paint {
  shade: Color     // only :red, :green, or :blue
}

cream = Paint { shade: :red }

Use a symbol set wherever you'd reach for an enum in another language: severity levels, edge kinds, named layout modes, the eight chart palette hues, …

When to use which

WCL has three closely-related tools for "a value that is one of a set of names". The right pick depends on whether the vocabulary is open and whether each variant carries data.