From: "Mehr, Assaph (Assaph)" <assaph@...>
Date: 2004-03-31T14:56:22+09:00
Subject: Re: Syntax: eval( "a = !a) != eval( "a = not a")

> Is there a reason why eval( "a = not a") raises a syntax error
> whereas eval( "a = !a") works as I expected ?

Probably because the statement "a = not a" is also a syntax error
(regardless of the eval).
The 'not' operator has a lower precedence than assignment, whereas the !
operator has a higher precedence. Therefore the interpreter reads the
second form as "a = not" which is a syntax error.
If you really want to use the word form use: eval("a = (not a)"), which
will take care of precedence.

See:
http://phrogz.net/ProgrammingRuby/tut_expressions.html#definedandorandno
t
and  http://phrogz.net/ProgrammingRuby/language.html the section on
Boolean Expressions and table_18.4.