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From: Bart Schaefer <schaefer@brasslantern.com>
Message-id: <110513213633.ZM13611@torch.brasslantern.com>
Date: Fri, 13 May 2011 21:36:33 -0700
In-reply-to: <BANLkTimXmy78=PFk_5Hm0j+4owt0Fb=BNg@mail.gmail.com>
Comments: In reply to Mikael Magnusson <mikachu@gmail.com>
 "Infinite recursions in math evaluation" (May 13, 11:37pm)
References: <BANLkTimXmy78=PFk_5Hm0j+4owt0Fb=BNg@mail.gmail.com>
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To: zsh workers <zsh-workers@zsh.org>
Subject: Re: Infinite recursions in math evaluation
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On May 13, 11:37pm, Mikael Magnusson wrote:
}
} [...]  Aha, actually a=a; $(( a )) crashes in the same way. (On
} a machine with a presumably less optimized/buggy compile, it does
} print "zsh: math recursion limit exceeded" instead of crashing). Is it
} simply a user error? I wouldn't expect either of these expressions to
} recursively look up values of the parameter until it encountered a
} number, but this is indeed what happens:
} % a=b; b=c; c=d; d=e; e=f; f=5; echo $(( a ))
} 5
} bash does the same...
} 
} I scanned quickly through the "Arithmetic Evaluation" section and
} found nothing suggesting that this should happen.

It's implicit in this:

    Named parameters and subscripted arrays can be referenced by name
    within an arithmetic expression without using the parameter expansion
    syntax.  For example,

        ((val2 = val1 * 2))

    assigns twice the value of $val1 to the parameter named val2.

"The value of $val1" in an arithmetic context is the result of doing
arithmetic evaluation on whatever is stored in the parameter.  If
that's the name of another (or even the same) parameter, then ...