OpenEuphoria

Re: pbr vs multiple returns

• Posted by Tommy Carlier <tommy.carlier at telenet.be> Jan 11, 2007
• 558 views

Chris Bensler wrote:
> I would definitely agree that PBR shoud be defined by both the callee and
> caller.
> I'm not very convinced that PBR is nessecary though.
> 
> Other than convenience and a slight improvement to readability (which is
> debatable
> IMO), can someone please explain how PBR would be useful compared to multiple
> return values? It aint clicking for me. Optimization?
> 
> Also, regarding multiple return values. What is the purpose of providing an
> alternate syntax for multiple return values?
> I don't see the purpose of introducing a new syntax to declare that a function
> returns multiple values. We can already do that by returning a sequence. All
> we need is a syntax for how to assign the members of a returned sequence to
> multiple variables.
> 
> {err,val} = get("3.14")
> 
> Shouldn't that be a viable statement without having to modify how get() works?
> 
> In anycase, I would whole heartedly agree with the syntax I demonstrated for
> multiple return values. I would rather not be required to use a special syntax
> to declared that a function returns multiple values. I don't see much point
> in it other than to force the caller to assign the result to multiple
> variables,
> instead of to a sequence if they wanted.

I also think the assignment of multiple values would be great. It would make
Euphoria
more functional. The stack code could look like this:

-- pushes o onto stack, and returns stack
function push(sequence stack, object o)
    return append(stack, o)
end function

-- pops an object from the stack, and returns {stack, popped_object}
function pop(sequence stack)
    return { stack[1..$-1], stack[$] }
end function

sequence s
object o
s = {}
for i = 1 to 10 do
    s = push(s, i)
end for

for i = 1 to 10 do
    {s, o} = pop(s)
end for

That said, I also like the idea of PBR. I agree with Matt, that
both the caller and callee have to specify the passing by reference.
I don't really like the * notation of C/C++ (and OOEU?). I quite like the
way it's done in C#, via the 'ref' keyword. In Euphoria, it could look like
this:

procedure swap(ref object o1, ref object o2)
    object o
    o = o1
    o1 = o2
    o2 = o
end procedure

integer a, b
a = 1
b = 2
swap(ref a, ref b)

The stack code could look like this, with PBR:

procedure push(ref sequence s, object o)
    s = append(s, o)
end procedure

function pop(ref sequence s)
    object o
    o = s[$]
    s = s[1..$-1]
    return o
end function

sequence s
object o
s = {}
for i = 1 to 10 do
    push(ref s, o)
end for

for i = 1 to 10 do
    o = pop(ref s)
end for

To be honest, I actually like this PBR

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