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

[Aleksej Saushev <asau%inbox.ru@localhost>]

Matt Sporleder <msporleder%gmail.com@localhost> writes:

>> On Mar 13, 2016, at 8:36 AM, Aleksej Saushev <asau%inbox.ru@localhost> wrote:
>> 
>> 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.
>
> Is $(( )) lisp mode or arithmetic mode?

Are "&&" and "||" arithmetic expressions or ones of more general kind?


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