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Using and Porting GNU Fortran

21.2.11.3 Bizarre Free-form Hollerith Constants

Last I checked, the Fortran 90 standard actually required the compiler to silently accept something like

FORMAT ( 1 2 Htwelve chars )

as a valid FORMAT statement specifying a twelve-character Hollerith constant.

The implication here is that, since the new lexer is a zero-feedback one, it won't know that the special case of a FORMAT statement being parsed requires apparently distinct lexemes `1' and `2' to be treated as a single lexeme.

(This is a horrible misfeature of the Fortran 90 language. It's one of many such misfeatures that almost make me want to not support them, and forge ahead with designing a new "GNU Fortran" language that has the features, but not the misfeatures, of Fortran 90, and provide utility programs to do the conversion automatically.)

So, the lexer must gather distinct chunks of decimal strings into a single lexeme in contexts where a single decimal lexeme might start a Hollerith constant.

(Which probably means it might as well do that all the time for all multi-character lexemes, even in free-form mode, leaving it to subsequent phases to pull them apart as they see fit.)

Compare the treatment of this to how

CHARACTER * 4 5 HEY

and

CHARACTER * 12 HEY

must be treated--the former must be diagnosed, due to the separation between lexemes, the latter must be accepted as a proper declaration.