These are the instances for the type variable in the rules.

A class is generic if it declares one or more type variables.

It defines one or more type variables that act as parameters.

In the later form, the side effect invisibly takes care of all places where a type variable is used.

In that case a type variable would be the return value:

These type variables are known as the type parameters of the class.

The necessity of this restriction is introduced the section on free type variables.

It makes possible the use of this type variable in class members instead of actual types.

There can be more than one type variable, in which case they are declared in a comma-separated list.

Let the type variable a denote the type of elements in the lists.

Standing alone, a type variable is meant to be as concrete as or , and clearly different from both.

Even if the notation uses typed variables, variables of that type may be used.

Future and promise typed variables are used to implement data-flow synchronization.

In the case of constructor, type variables are declared before the constructor name.

Languages that support existential types make use of existentially quantified type variables.

Parametric polymorphism necessitates the introduction of type variables, which range over all types.

I.e. in context of the example, the same type variable appears both bound and free in different types.

As a consequence, a free type variable cannot be interpreted better than stating it is a monotype without knowing the context.

Only if it contains another qualified type variable, the specialization could continue further replacing for it.

This is achieved by adding constraints to type variables in parametrically polymorphic types.

If we then pick non-selective education as the base for comparison in the school type variable, we will almost certainly avoid negative relationships.

In this case the type variable is appended by the keyword followed by a name of the class or the interface.

Scheme uses strictly but dynamically typed variables and supports first-class functions.

Programming languages that support parametric polymorphism make use of universally quantified type variables.

A type variable is an unqualified identifier.