08-291
To: J3
From: Malcolm Cohen
Subject: Intrinsic inquiry functions in init exprs
Date: 2008 November 04


1. Introduction

The definition of specification inquiry has changed between F2003 and the
F2008 draft.  It now includes functions that it ought not to.


2. Discussion

Informally, inquiry functions were things that are supposed to be "safe".
We actually say
  "whose result depends on the properties of one or more of its arguments
   instead of their values".
Unfortunately, we have gone ahead and classified several argumentless
intrinsic functions as "inquiry", which not only fails to satisfy the
definition, but allows them to appear in initialization expressions even
though their values are not compile-time determinable.

The functions in question are:
  COMMAND_ARGUMENT_COUNT()
  THIS_IMAGE()

Note that COMMAND_ARGUMENT_COUNT was faulty in F2003 also in that it did
not satisfy the definition of an inquiry function.  However, it was not
permitted in an initialization expression so this was not a critical flaw.

Furthermore, the classification of intrinsic procedures omits the case of
"pure subroutine".  This ought to be repaired.


3. Strategies for repair

There are several different ways that these functions could be prohibited
from appearing in initialization expressions, but that would still leave
the contradiction between the definition of "inquiry" in 13.1 and the
function classifications.

Therefore these functions should be reclassified.  The simplest
reclassification is as transformational; that still requires (very few)
words in the definition of an initialization expression to exclude them.

An alternative strategy would be to notice that the classification
"transformational" serves three conflicting purposes:
 (1) allowance in init exprs when all arguments are init exprs;
 (2) "miscellaneous" category catching all functions not suitable for
     inquiry or elemental;
 (3) doing something transformational producing or consuming an array:
     this is what the actual definition (and the name) alludes to!
If we had a good name for (1), we could use "miscellaneous" or "other" for
(2) ... and ignore (3) because that aspect isn't used except to confuse
the reader.

A third strategy would be to keep the name "transformational" for item (1),
and to introduce a different term for the problematic functions.  This
could be "environmental", "runtime" or simply "miscellaneous".


4. Edits for simple repair strategy

[150:7.1.12p1(6)] Change "other than NULL" to
  "other than COMMAND_ARGUMENT_COUNT, NULL, and THIS_IMAGE".
{Argumentless transformationals need exclusion from this item.}

[313:13.1p1] Replace the whole paragraph with
  "Intrinsic procedures are divided into six classes: inquiry functions,
   elemental functions, transformational functions, elemental subroutines,
   pure subroutines, and (impure) subroutines."
{Improve wording as well as listing all the actual classifications we use.
 The word "impure" is parenthesised to indicate that we don't use the word
 in the classification, but that it is nonetheless the case.}

[316:13.5p2] "a subroutine but not pure" -> "an impure subroutine".
{Random wording improvement.}

[317:13.5 Table 13.1, COMMAND_ARGUMENT_COUNT entry] "I" -> "T".
{Change class.}

[322:13.5 Table 13.1, both THIS_IMAGE entries] "I" -> "T".
{Change class.}

[337:13.7.37p2] "Inquiry" -> "Transformational".
{Change class of COMMAND_ARGUMENT_COUNT.}

[337:13.7.164p2] "Inquiry" -> "Transformational".
{Change class of THIS_IMAGE.}


5. Edits for third repair strategy

These edits choose "miscellaneous functions" to classify intrinsic
functions that are not suitable for inclusion in an initialization
expression.  We don't absolutely need a definition (the normal English
meaning is being used), but one is provided for clarity.

[311:13.1p1] Replace the whole paragraph with
  "Intrinsic procedures are divided into seven classes: inquiry functions,
   elemental functions, transformational functions, miscellaneous
   functions, elemental subroutines, pure subroutines, and (impure)
   subroutines."
{Improve wording, list all the actual classifications we use, add new
 class.}

[313:13.1p2] Change "All other" -> "Some".
             Before "All standard" insert
  "Other intrinsic functions are classified as <<miscellaneous>>."
{Not all other intrinsic functions are transformational; add sentence
 about miscellaneous.}

[316:13.5p2] In the description of the Class column, add new item
  alphabetically
    "M indicates that the procedure is a miscellaneous function".

[316:13.5p2] "a subroutine but not pure" -> "an impure subroutine".
{Random wording improvement.}

[317:13.5 Table 13.1, COMMAND_ARGUMENT_COUNT entry] "I" -> "M".
{Change class.}

[322:13.5 Table 13.1, both THIS_IMAGE entries] "I" -> "M".
{Change class.}

[337:13.7.37p2] "Inquiry" -> "Miscellaneous".
{Change class of COMMAND_ARGUMENT_COUNT.}

[337:13.7.164p2] "Inquiry" -> "Miscellaneous".
{Change class of THIS_IMAGE.}

===END===