Why Java Doesn't Need Operator Overloading (and Very Few Languages

[Yigal Chripun]

On 16/04/2009 15:47, Daniel Keep wrote:
>
> Yigal Chripun wrote:
>> On 15/04/2009 18:50, BCS wrote:
>>> Hello Yigal,
>>>
>>>
>>>> sounds silly to me. Why not simply generalize and allow
>>>> defining in-fix functions like in functional languages? that
>>>> also includes allowing any unicode character[s].
>>> lexing and (more importantly) parsing become a major problem if
>>> you allow that
>>>
>>>
>> Since it is done in other languages (for example Scala), I'm sure
>> it's not impossible to implement. I don't think Scala is that much
>> more troublesome to lex/parse.
>
> That's not a very good argument.  Lots of things are possible;
> doesn't mean they're a good idea.
>
> Operator precedence determines how expressions are parsed.  Having
> user-defined operators would require the code to be parsed once to
> get the operator definitions, then re-parsed with a different
> meaning.  Euch.
>
> That said, I'm OK with adding operators with well-defined meanings
> to the language on an as-needed basis.  opDot, opUnion, opCross,
> etc.
>
> -- Daniel

say we have the expression  (2 + 3 foo 4) (foo is infix function).
Scala parses this as: 2 + 3.foo(4) so there is no parsing problems with
this.
see http://www.scala-lang.org/node/118

Eiffel is similar (also an OOP approach):
2 + 4 is the same as 2.plus(4)
the definition of plus is (alias is used to specify the operator):

> plus alias "+" (other: INTEGER): INTEGER
>         -- ... Normal function declaration...
>     end

from wikipedia for Eiffel:
>
> The range of operators that can be used as "alias" is quite broad;
> they include predefined operators such as "+" but also "free
> operators" made of non-alphanumeric symbols. This makes it possible
> to design special infix and prefix notations, for example in
> mathematics and physics applications.
>
> Every class may in addition have one function aliased to "[]", the
> "bracket" operator, allowing the notation a [i, ...] as a synonym for
> a.f (i, ...) where f is the chosen function. This is particularly
> useful for container structures such as arrays, hash tables, lists
> etc.

in Haskell you can define both precedence and associativity for 
operators. I don't know Haskell but found this link which explains the 
syntax:
http://www.haskell.org/tutorial/functions.html
I guess we need someone who knows Haskell to explain how they 
implemented this.