The construct

        type_expression$operation_name

denotes the component named "operation_name" from the specified type.
Selection binds more tightly than application.  Thus the type_expression
should be parenthesized if it contains any function applications.

A selection may optionally be followed by

        << signature >>

to indicate which, of a number of identically named components with
differing signatures, was intended.  Thus if T is declared to be

        Array[10, Float]

then

        T$. <<func[var T; val Short] var Float>>

denotes the "variable returning" subscription operation, as opposed to

        T$. <<func[val T; val Short] val Float>>

which denotes the "value returning" one.

The signature of the selection is that of the type component, with occurrences
of the local type identifier replaced by the type_expression.