To: J3                                                     J3/19-249
From: Van Snyder
Subject: Syntax for True Enumeration types
Date: 2019-October-16
Reference: 19-231r2, 19-232

1. Syntax to define an enumeration type
=======================================

1.1 General idea

  <begin type definition>
    [ PRIVATE ]
    <list enumerators>
  <end type definition>

1.2 Begin and end type definition

Based on ENUM in subclause 7.6

  ENUM [[, INITIAL ( <enumerator-name ),  <access-spec> ] ::] <type-name>
    ...
  END ENUM [ <type-name> ]

1.3 Declare enumerators

A statement to specify enumerator names

  ENUMERATOR [ [, <access-spec> ] :: ] <enumerator-name> &
    & [ , <enumerator-name> ] ...

{Simply listing the names without a keyword does not work. In fixed
form, or if the optional space in END TYPE is omitted, the ENDTYPE
statement looks like just another enumerator.}

1.4 Declare default initial value

On the statement that introduces the type definition

  ENUM [, INITIAL ( <enumerator-name> ), <access-spec> ] :: <type-name>

2. Syntax to declare an object of enumeration type
==================================================

  TYPE ( <type-name> ) [[ , <attr-list> ] :: ] <entity-decl> [ = &
    & <enum-expr> ]

3. Syntax to reference an enumerator
====================================

Straw vote on 19-231 was that enumerators are class (2) names.

Therefore, the type name must always appear.

Vauguely reminiscent of component selection

  <type-name> % <enumerator-name>

{We do not ever use "<type-name> %" for anything.}

4. FIRST, LAST inquiry
======================

Vaguely reminiscent of type parameter inquiry

  <enumeration-type-object> % FIRST
  <enumeration-type-object> % LAST

5. NEXT, PREV as type-bound functions
===========================================

NEXT and PREV are considered to be type-bound functions that are
defined by the type definition, without bindings being declared.  There
is no syntax provided to declare procedure bindings.

  <enumeration-type-object> % NEXT ( [ [ STAT= ] <stat-variable> )
  <enumeration-type-object> % PREV ( [ [ STAT= ] <stat-variable> )