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Re: Nasty language semantics (Was: error message I don understand) [message #174911 is a reply to message #174909] Sun, 17 July 2011 18:26 Go to previous messageGo to previous message
Robert Heller is currently offline  Robert Heller
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At Sun, 17 Jul 2011 19:47:12 +0200 August Karlstrom <fusionfile(at)gmail(dot)com> wrote:

>
> On 2011-07-17 18:31, Peter H. Coffin wrote:
>> On Sun, 17 Jul 2011 16:50:28 +0200, August Karlstrom wrote:
>>
>>> On 2011-07-17 15:03, Jerry Stuckle wrote:
>>>
>>>> This isn't mathematics - it is programming, as people have told you
>>>> before. If you want mathematics, get a chalkboard.
>>>
>>> Don't be silly. There are several programming languages in which `='
>>> denote (surprise) equality.
>>
>> Very few that use it alone.
>
> Pascal, Modula-2, Eiffel and Ada all use `=' for equality and `:=' for
> assignment.

Also: don't forget Basic. Basic uses '=' for both equality
AND assignment, but you cannot perform an assignment someplace where a
logical (or any other) expression might occur, so there is no ambiguity.

>
>> They may set the context with a previous
>> "LET" or "test" or a grouping indicator, or, if they don't, they have
>> very rigorous typing such that assignments are statements alone and do
>> NOT return anything that could possibly be used in a logical/comparative
>> way, not even a success or failure.
>
> Yes, and for a good reason - the statement-expression separation (or
> maybe we should say side-effect free expressions) is related to the
> sound principle of command-query separation.
>

Also: C++ allows a function call that returns a reference on the
left side of an assignment. This the statements:

int & something(int bar);

if (something(4) = 3) {
}

would NOT be an error, although it is not obvious what is going on.

> August
>

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Robert Heller -- 978-544-6933 / heller(at)deepsoft(dot)com
Deepwoods Software -- http://www.deepsoft.com/
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