Re: Results of || and && operators in /bin/sh $(( )) evaluation

[Matt Sporleder <msporleder%gmail.com@localhost>]

> On Mar 13, 2016, at 8:36 AM, Aleksej Saushev <asau%inbox.ru@localhost> wrote:
> 
>  Hello,
> 
> Robert Elz <kre%munnari.OZ.AU@localhost> writes:
> 
>> Currently, NetBSD's /bin/sh (all versions since $(( )) was added, back
>> in 1994 it seems) calculate the result of
>> 
>>    x && y
>> 
>> as 0 if x == 0, otherwise y, and calculate
>> 
>>    x || y
>> 
>> as x if x != 0, and as y otherwise.
>> 
>> That is, 3 && 4 evaluates to 4, and 3 || 4 evaluates to 3.
>> 
>> In C, these operators always produce 1 or 0 (true or false), regardless
>> of the values of the operands.
>> 
>> So does every other shell I can find to test.
>> 
>> I have just submitted PR bin/50960 about this issue (and it would probably
>> be better if you replied to that PR, rather than this e-mail).
>> 
>> I have a fix, it is trivial, but I don't want to implement if someone
>> in the NetBSD community (or more importantly, something in the system) is
>> relying upon this odd behaviour.
> 
> It is not odd, it follows well-established long-standing tradition that
> is reflected in, e.g.:
> 
> "AND evaluates each [expression] until a value of NIL is found or the
> end of the list is encountered. If a non-NIL value is the last value it
> is returned, or NIL is returned."
> 
> "...expressions which are evaluated in order of their appearance. When
> one is found to be non-NIL it is returned as the value of OR. If all are
> NIL, NIL is returned."
> (The Standard Lisp Report, ca. 1982)
> 
> "If all forms but the last evaluate to true values, <<and>> returns the
> results produced by evaluating the last form."
> 
> "If the evaluation of any form other than the last returns a primary
> value that is true, <<or>> immediately returns that value..."
> (Common Lisp HyperSpec, 1996)
> 
> "If every form but the last evaluates to a non-nil value, <<and>> returns
> whatever the last form returns."
> 
> "If any form other than the last evaluates to something other than nil,
> <<or>> immediately returns that non-nil value without evaluating the
> remaining forms."
> (Common Lisp the Language, 2nd ed., 1994)
> 
> "The <test> expressions are evaluated from left to right, and the value
> of the first expression that evaluates to a false value (see [Booleans])
> is returned. Any remaining expressions are not evaluated. If all the
> expressions evaluate to true values, the value of the last expression is
> returned."
> 
> "The <test> expressions are evaluated from left to right, and the value
> of the first expression that evaluates to a true value (see [Booleans])
> is returned."
> (Revised^4 Report on Scheme, 1991)
> 
> I don't have earlier references at hand.
> 
> 
> -- 
> HE CE3OH...
> 

Is $(( )) lisp mode or arithmetic mode?