functions with named parameters and default values

[Răzvan Rotaru]

Hi,

I'm trying to find a way to have named parameters in functions. Intuitively, structures with destructuring bind can be used for that:

> myfunction {a, b, c} = println (a+b+c)
myfunction is {
   .a is number,
   .b is number,
   .c is number
} -> () = <code$myfunction>
> myfunction {a=100, b=50, c=99}
249

Can I somehow specify default values for parameters?

Cheers,
Razvan

[chrisichris]

Hi, 

you can use a list of variants:

myFn params = 

  (var a = 100; 

  var b = 50;

  var c = 10;

  for params \case of

     A n: a := n;

     B n: b := n;

     C n: c := n;

  esac;

  println (a + b + c));

myFn [A 20, C 10];

This is often used in the eval module: http://dot.planet.ee/yeti/docs/latest/yeti.lang.compiler.eval.html

Another thing you could do especially when there are many options is define a default structure

> defS = {a = 10, b = 20, c = 30}

> mFn {a,b,c} = println (a + b + c)

> mFn (do x: x with {a = 100} done defS)

the last call looks a bit strange but the with in a funciton makes sure that you only override fields which are in the struct

[Răzvan Rotaru]

Thanks,

The first option would work, even though it's not as nice as destructuring bind with structures (and it requires more typing). The second option puts the burden in the hands of the caller, which not something I would like to do.

Cheers,
Răzvan

[Răzvan Rotaru]

Would it be possible/difficult to add default values to structures?

Răzvan

[Madis]

On Tue, 13 Jan 2015, Răzvan Rotaru wrote:

> Would it be possible/difficult to add default values to structures?

Possible yes, I considered it at some time, but imho variant lists do the
same job in more flexible way - for example you can construct the optional
parameter list dynamically at runtime. Yes it's a bit more work inside the
function, but then it would be more useful to add mechanism for doing that
parameter extraction in less code. In the end, it would be more useful to
add some kind of compile-time macros to the language, but that's probably
not going to happen now.

[Răzvan Rotaru]

My main worry with variant lists is that you have to process them sequentially, i.e. I can't have direct access to the value of one parameter. And this processing requires state.

Razvan