Re: ALGOL - lexical analyzer

  nmm1@cus.cam.ac.uk (Nick Maclaren) wrote:
> [Algol 60 had a well-defined display representation suitable for
> printing in magazines, with keywords in boldface, but it was about 35
> years too early for computers to do that. Some implementations
> reserved the keywords, e.g. BEGIN and END which was wrong since you
> were allowed to have variables called begin and end, others did gross
> things like quoting them all, e.g., 'BEGIN' and 'END' which was
> unusable. I can't lay my hands on my Algol68 report but as I recall
> they avoided that mistake and defined it in a single ASCII-ish
> character set. -John]


This interesting question came up in the Unicode list resently. I found a
reference that describes it correctly:
          http://en.wikipedia.org/wiki/ALGOL


In short, the ALGOL uses boldface the same way one does in pure
mathematics, i.e., it changes the semantics. Because of this semantics
change in pure math, different letter styles was added to Unicode
(thanks to Ken Whistler willing to listen to my explanations). It
means that ALGOL can now be implemented correctly, using the Unicode
chracter set. This is otherwise one of the few instances of computer
code where rendering style of letters affect the semantics. Past ALGOL
compiler writers, not having access to a character set differing
between bold and plain letters, had to improvise something.
--
    Hans Aberg

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