[Gambas-user] [SPAM] Re: Ambiguous expression?

[Dag Jarle Johansen]

Sorry
this i mathe
if you have been on a highschool or a college, you would know: it's easy
multiplication and diviation goes for addition and subtsraction.
Gambas works like this, if you are unsure, use parantesis ()

regards,
Dag-Jarle Johansen


Am Mittwoch, den 10.03.2010, 20:20 +0100 schrieb Doriano Blengino:
> Benoît Minisini ha scritto:
> >> Alessandro Rinaldi ha scritto:
> >>     
> >>> I really think yes.
> >>> Standard symbol for fractions is /, why should you use \?
> >>>       
> >> Backslash is "integer division", and should yeld an integer result.
> >> Slash is "float" division, and yelds a float number (this is "Basic"
> >> syntax; other languages use different methods).
> >>
> >> The expression "1\2*3" is not really ambiguous, it is only for Gambas
> >> (don't ask me why); it should be seen as "take an integer number,
> >> integer-divide it for another integer number, and multiply the result
> >> for another integer number, giving an integer result".
> >>
> >>     
> > I noticed that operator evaluation order differ between languages, even if 
> > they agree on most parts.
> >
> > So I decided to raise an error when the compiler encounters different 
> > operators having the same evaluation order weight, and when I thought that the 
> > interpreter may not do what the user thinks.
> >
> > By compelling the user to add brackets, I make the source code less ambiguous 
> > for another reader, so this is a good thing.
> >
> > But the test is not perfect, and I don't remember why I do not raise the error 
> > for 1/2*3 and I raise it for 1\2*3.
> >
> > Maybe because that mixing "*" and "/" is usual in mathematics, but mixing an 
> > integer division with a normal multiplication not, and I wanted to force the 
> > use of brackets.
> >   
> Perhaps this is because C has "/" and "*", and both have a double 
> meaning (integer and float);
> pascal has two separated "/" and "DIV", and only one "*". So gambas is 
> similar to pascal.
> When an operator is the same on different types (integer and floats), 
> the compiler checks the arguments of the operator to decide whether 
> promote one of the two (and the result).
> In this very case, all the arguments are integer, so all the operators 
> are integer too, and there should be no doubt.
> Anyway, division and multiplication have the same precedence and 
> (probably?) same associativity.
> 
> But I agree with you: by combining precedence and associativity it is 
> easy to make up a mess, and sometimes a solution like yours is better. 
> The C language has something like 15 or more rules, so who remembers the 
> exact result of "*pointer-- >> 3+1"?
> > Morever, that error is actually just a warning. I can suppress it, and Gambas 
> > will just apply its operator evaluation order without telling anything. But I 
> > don't think I will do it!
> >
> >   
> Uhm... *it is* an error if the compiler refuses to compile... it would 
> be possible to turn it in a warning (does gambas have warnings?), if 
> only one is very sure about promoting. But gambas uses a typing scheme 
> different from C and pascal, and automatic type conversions, so you are 
> probably right in keeping your way.
> 
> Regards,
> Doriano
> 
> 
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