Pretty please: Named arguments

[spir]

On 03/02/2011 02:59 PM, Steven Schveighoffer wrote:
> On Wed, 02 Mar 2011 08:45:43 -0500, Jason E. Aten <j.e.aten at gmail.com> wrote:
>
>> I find this an interesting discussion. Coming from writing alot of code in
>> language that makes extensive and
>> highly effective use of named arguments (R), I can say that optional named
>> arguments
>> (as in Lisp, and descendants like Python and R) do have big software
>> engineering benefits,
>> but also come with a substantial costs in terms of complexity of the
>> function call sequence.
>>
>> That is, named arguments can be expensive in a typical interpreted
>> implementation
>> (probably one reason why R and Python are much slower to execute than the
>> other
>> interpreted languages), presumably because each function call has to
>> invoke hash
>> table lookups to determine the canonical formal position of each actual
>> argument, and deal with variadic
>> cases, to rearrange the order of the arguments to match expectations of the
>> callee.
>>
>> Someone familiar with lisp compilers could probably tell you if the heavy
>> speed tax is intrinsic
>> or just the price of interpretation.
>>
>> It would indeed be an interesting challenge to see if the compile-time
>> metaprogramming
>> features of D would allow one to include named arguments in an opt-in
>> fashion without speed reduction.
>
> Considering that calling a function with parameters by name directly translates
> at compile time to a function call by position, there should be zero speed
> impact. The interpretation of the parameter names, which is done at runtime for
> Python, would be done at compile time in D.
>
> -Steve

I had never thought at that, but I'm surprised: what prevents Python's 
"compiler" (say, a semantic phase after parsing) to check number and names of 
arguments. (Number seems not to be checked before runtime neither.)
All required information is in the AST. For named params, Python could 
translate to position params just like D. This would certainly remove a 
relevant amount of runtime "speed-down", I guess. (Only type-check of builtin 
func args must remain at runtime.)

Denis
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