Type Definition

A type definition defines a new generic type. The syntax is

deftype quantifiers name(parameters) = type;

The quantifiers are the same as for a declaration. The parameters are type parameters introduced in the quantifiers.

For example

deftype for_type s, t: Pair(s, t) = Tuple(s, t);

defines type Pair as a tuple of two elements, each with its own type.

Another example is the definition of a uniform vector. Given type definition

deftype for_unit a, for_index X: UniformVector(a, X!) = a*X!;

the following fails

declare foo :: UniformVector(metre, Geom3!);

define foo =
    vector3d(1, 2, 3);

Function vector3d creates vectors with uniform unit of measurement, but no units are provided. The actual derived type is UniformVector(1, Geom3!). A proper definition is

define foo =
    vector3d(1*|metre|, 2*|metre|, 3*|metre|);