Re: replace() and replace-with()

On Thu, Dec 3, 2020 at 8:03 AM Michael Kay <mike@saxonica.com> wrote:

>
>    1. Is this definition of one function or of four functions? If this is
>    a definition of one function, then how do we know that we have seen all of
>    the definitions (maybe there are more than 4 definitions, but they are
>    scattered across the code and we cannot be aware of all of them)?
>
>
> It is one function. The arity is two. All the keyword arguments in the
> call are combined into a single map value passed to the function
>

The first two arguments are $input and $pattern.

A replace()  function is meaningless without providing a replacement, so
the arity should be at least 3.

So, I am even further confused by this answer. Are you proposing a new
function when you don't know what its arity is?

Sorry if this is a rather harsh reaction, but better hear it from one
person now, than from many people when it is too late.

Thanks,
Dimitre


>
>    1.
>    2. What is the arity of the function: 2 or 3 or 4 or 5 or 6? If the
>    answer is 2, how can you explain to a developer that in all the above cases
>    they are calling a 2-argument function, when they in fact are literally
>    specifying 3 and 4 arguments?
>
>
> It depends on the developer. If they use Python, they will already be
> familiar with the idea of ** arguments:
>
> def intro(**data):
>     print("\nData type of argument:",type(data))
>
>     for key, value in data.items():
>         print("{} is {}".format(key,value))
>
> intro(Firstname="Sita", Lastname="Sharma", Age=22, Phone=1234567890)
> intro(Firstname="John", Lastname="Wood", Email="johnwood@nomail.com", Country="Wakanda", Age=25, Phone=9876543210)
>
> (Here type(data) outputs <class dict>)
>
> If they're familiar with varargs in Java, then I would explain it as
> saying it's very similar to varargs: there's one parameter defined in the
> declaration, which receives a composite value from several arguments
> supplied independently in the call.
>
>
>    1. What if some of the keyword arguments are mutually exclusive and
>    thus shouldn't be specified together on the same function call? Or if we
>    have two different subsets of keyword arguments that are mutually
>    exclusive? How can one specify this formally?
>
> We could try and add that mechanism, but I think it's probably OTT. I
> don't see such a mechanism in Python, for example. It's not unusual to have
> preconditions on the valid arguments for a function beyond those that can
> be expressed formally in the function signature.
>
>
> Such deep changes need scrupulous attention and discussion, so, please, go
> gradually, patiently, step by step, and only proceed deeper if you have got
> a near-consensus at the current step.
>
>
> Personally, I find it hard to assess the steps without seeing where they
> lead. I can only judge whether the feature seems to "work" by defining it
> fully and trying it out. The only way to judge whether this mechanism for
> keyword arguments is useful is to design some functions that take advantage
> of it and see whether they appear usable. That's what I've been trying to
> do.
>
> Michael Kay
> Saxonica
>
>

-- 
Cheers,
Dimitre Novatchev
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