Re: Why does the lexer convert text integer lexemes to binary integers? I thought that lexers should be simple?

On Monday, July 18, 2022 at 9:30:51 AM UTC-7, gah4 wrote:


(snip, or moderator wrote)


> [In my experience separating the lexer from the parser makes it a lot easier
> to deal with common lexical situations like skipping white space and comments.
> You could certainly do that in a combined scheme but I'm not sure it would end
> up any simpler. -John]


Interesting. As I previously noted, STEP mostly doesn't do a separate lexical analysis.


It does, however, do three things before the macros see the input: convert multiple
blanks to a single blank, pass apostrophed strings through whole, and remove
comments delimited by double quotes.


Apostrophed strings are slightly more interesting. Internal double apostrophes
are converted to single apostrophes, and the delimiting apostrophes are
converted to a special character that isn't an input character.


One of my projects 45 years ago, was to write macros to recognize the
syntax of IBM OS/360 Fortran IV. Direct access I/O statements use
a single apostrophe to delimit the record number:


            READ(1'N) X,Y,Z


There is no way to write macros for that syntax after the previous processing.


Much fun figuring out all the strange things done in programming language
syntax over the years.

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