Add more rules on preprocessor expressions and their types #16
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Change all preprocessor expressions for #if, #elif to evaluate to integer values. Define the relationship of Fortran logical constants and operators to their C counterparts. Addresses #14.
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Thanks for making a great start on this!
This is a non-trivial change and I have a correspondingly large amount of feedback. I may have even more feedback after further updates and further thought.
However I think we're on the right track here, and as I've already said I really want to see us adopt the core changes proposed in #14.
| 'true'. | ||
| 10 .FALSE. is treated as the integer 0. .TRUE. is treated as the | ||
| integer 1. | ||
| 11. Undefined identifiers are treated as zero, as in CPP. |
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Minor clarification, inspired by C spec wording:
| 11. Undefined identifiers are treated as zero, as in CPP. | |
| 11. Any undefined identifiers that remain after macro expansion (including those | |
| lexically identical to keywords or intrinsics) are treated as zero, as in CPP. |
| 15. Integer expressions in preprocessor directives are calculated in | ||
| the maximum precision the processor supports. (There are no KIND | ||
| specifiers on integer constants in the preprocessor.) |
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This feels like it should be two separate rules. IIUC the parenthetical is actually prohibiting certain syntax, so it should not be parenthetical.
| 13. The Fortran operators .AND., .OR., ,NOT., .EQ., .NE., .EQV., and | ||
| .NEQV. calculate the save values as the C operators &&, ||, !, ==, | ||
| !=, ==, and !=, respectively. |
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Here you're assuming we also accept the suggestion in issue #13 to add these additional Fortran operators to the draft. If we were to merge this PR alone as-is, these new rules would be inconsistent with the earlier list of operators.
This PR purports to address only #14 (which IMO has a strong stand-alone motivation), and I'd like to keep it focused on that proposal without conflating the orthogonal issue #13 (where the motivation may be seen as potentially weaker).
Please decouple these two PRs. I suggest removing the "new" operators above and getting this PR into a mergeable state to address solely #14, and then PR #15 can later introduce the obvious extension for the operators proposed by #13.
| 13. The Fortran operators .AND., .OR., ,NOT., .EQ., .NE., .EQV., and | |
| .NEQV. calculate the save values as the C operators &&, ||, !, ==, | |
| !=, ==, and !=, respectively. | |
| 13. The Fortran operators .AND., .OR., ,NOT., =, /= evaluate to the same values as | |
| the C operators &&, ||, !, ==, and !=, respectively. |
| 14. The Fortran operators .LT., .LE., .GT., and .GE. calculate the | ||
| same values as the C operators <, <=, >, and >=, respectively. |
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Same comment here, please move this new rule to PR #15
| 14. The Fortran operators .LT., .LE., .GT., and .GE. calculate the | |
| same values as the C operators <, <=, >, and >=, respectively. |
| 12. C character constants (such as 'A', '\n') are treated as | ||
| integer values, as they are in C. |
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This run-on list of rules needs to be restructured to clarify that the rule above (and possibly others?) only apply to the conditional expression in #if/#elif. For example this does not impact macro expansion in source.
| 9. Expressions in #if and #elif directives evaluate to INTEGER values. | ||
| Zero values are treated as 'false'. Non-zero values are treated as | ||
| 'true'. |
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When it comes time to actually write spec wording for this, it's not enough to say the expression "evaluate to INTEGER values". There must be additional constraints to rule out (for example) character strings in preprocessor conditional expressions.
For now it might be sufficient to say something like
| 9. Expressions in #if and #elif directives evaluate to INTEGER values. | |
| Zero values are treated as 'false'. Non-zero values are treated as | |
| 'true'. | |
| 9. Expressions in #if and #elif directives must be integer constant expressions as in CPP | |
| (with the extensions described below), and evaluate to INTEGER values. | |
| As in CPP, zero values are treated as 'false'. Non-zero values are treated as | |
| 'true'. |
| 10 .FALSE. is treated as the integer 0. .TRUE. is treated as the | ||
| integer 1. |
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What about .false. and .true.?
Change all preprocessor expressions for #if, #elif to evaluate to integer values. Define the relationship of Fortran logical constants and operators to their C counterparts.
Addresses #14.