[parenscript-devel] Tweaks to the NOT and RETURN special forms

[Daniel Gackle]

I pushed another fix for PS LOOP, this time to make :WHILE and :UNTIL
clauses play well with :FOR clauses. Working on this, I noticed the
generated code was getting lots of expressions like "!!x". So I tweaked the
NOT special form to eliminate double negatives (this wasn't a big deal
because the NOT special form was already doing some operand reduction):

  (ps (not (not x)))
    now => "x;"
    formerly => "!!x"

Also, we sometimes get syntactically illegal double RETURNs in our generated
JS (things like "return return x;"). Although this only happens when we make
a mistake and use the wrong macro, it can be hard to track down the problem.
Since "return return" is never legal JS, I added an error check to the
RETURN special form to signal when PS is given such a bad expression to
compile.

(The above pertains to commit 7c417818 and its two predecessors.)

Daniel
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