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From: Paul Rubin <no.email@nospam.invalid>
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Subject: Re: Proliferation of Reserved Words
Date: Tue, 01 Jun 2021 00:40:50 -0700
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"Randy Brukardt" <randy@rrsoftware.com> writes:
> At least twice it was proposed that Ada have "keywords", identifiers with 
> special meaning in the syntax but that were not reserved.

I remember this as a fundamental decision of PL/I that made PL/I quite
hard to parse using the automata-based methods developed not long
afterwards.  I don't know what consequences that had for PL/I or
anything else, if any.  But I think it was retrospectively considered a
mistake.  It's a lot easier to separate parsing and scanning if you can
have reserved words.

OTOH I know that C compilers sometimes (usually?) handle typedefs by
having the parser tell the scanner to treat the typedef name as
keyword-like, after it sees that a typedef has been defined.