Variants

[
  Datatype variants
  Funcon   variant
  Funcon   variant-id
  Funcon   variant-value
]

Meta-variables
  T <: values

Datatype
  variants(T) ::= variant(_:identifiers, _:T)

A value of type variants(T) is a pair formed from an identifier and a value of type T.

Funcon
  variant-id(_:variants(T)) : =>identifiers
Rule
  variant-id(variant(I:identifiers, _:T)) ~> I

Funcon
  variant-value(_:variants(T)) : =>T
Rule
  variant-value(variant(_:identifiers, V:T)) ~> V