To:		WG5

From:		Lawrie Schonfelder

Subject:	Draft NP for TR2 on Data type enhancements



Title:		Enhancement of Fortran derived type facilities



Scope:  	This technical report defines the extensions to the syntax and

semantics of Fortran (as defined in the Fortran 95 standard) to extend to derived

types the facility of parameterisation similar to that already supported for

intrinsic types.  It also defines an extension allowing components of a derived

type to be allocatable.



Purpose and Justification:		A technical report of type 2 is being produced to

define the specific language extensions and to place these in the public domain. 

It is intended that these extensions will be included without change in a

subsequent revision of the Fortran standard, unless experience indicates that

there are inadequacies in the definition.  It is hoped that this will enable this

important facility to be defined more rapidly than would be possible in a single

step extension by full language revision.

	It is a major language irregularity in the current Fortran language that

while intrinsic types are parameterised, derived types cannot be.  As a result it is

very difficult to mix parameterised intrinsic types and derived types in the same

program.  This makes a number of important applications difficult to express in

Fortran.  There is, therefore, a pressing need to extend the derived type facilities

to correct this irregularity.  This extension also enhances the data abstraction

capability of the language in a way which is a step on route to adding "object

oriented programming" facilities to Fortran.

	The restriction which precludes components of a derived type from being

allocatable forces the use of pointer components even in applications which do

not need the general indirection capabilities of pointers.  This has a number of

serious implications for program efficiency.  there is a need for allocatable

components to provide for more efficient support for applications of this kind.



Implementation schedule:	A NP can be produced by the end of June'95, and

based on existing material already existing in the WG5 papers (references to be

researched) an initial WD could be available by a similar date.  It should be

possible to reach PDTR stage by Dec'95.