To: J3                                                     J3/23-191
From: Mark LeAir & Generics
Subject: F202Y Further Refinements of Lower Bounds in Requirements
Date: 2023-June-13

Reference: 23-155

Introduction
============

Paper 23-155 introduces the formal syntax for TEMPLATE and REQUIREMENT
which are two main constructs in support of the generic programming
feature proprosal for F202Y.

One unanticipated side-effect of the introduction of REQUIREMENT and
its associated REQUIRES statement is that it is possible to give multiple
distinct specifications of deferred constants that are consistent in terms
of type, kind, and shape, and yet differ with respect to their lower
bounds.

Currently, paper 23-155 solves this problem by allowing only default
lower bounds in REQUIREMENTS. However, the Generics Subgroup wishes to
deliberate further on this and possibly relax some associated constraints
so arbitrary lower bounds could be used in the REQUIREMENT construct.


An Example
==========

REQUIREMENT R1(C)
  INTEGER, CONSTANT :: C(*)
END REQUIREMENT R1

REQUIREMENT R2(C)
  INTEGER, CONSTANT :: C(2:*)
END REQUIREMENT R2

TEMPLATE A(C)
  REQUIRES R1(C)
  REQUIRES R2(C)
  CONTAINS
    SUBROUTINE SHOW()
      PRINT *, LBOUND(C) ! WHAT IS THE RESULT?
    END SUBROUTINE
END TEMPLATE A


Possible Solutions
=====================

Alternative 1: Do not allow the specification of the lower bound of a
               deferred constant in REQUIREMENTS.

Alternative 2: Require all lower bounds of a deferred constant to be
               consistent.

Alternative 3: Explicit declaration in the template scope determines lower
               bound.

Proposal
========

Generic Subgroup would continue to evaluate these alternatives for
inclusion in F202Y.

===END===