[TCLCORE] Request for comments: Stasher API changes

[Lars H. <Lar...@re...>]

Sorry to bother in the middle of the 8.6b2rc testing, but it seems to be 
longer than first expected. Also, I've been reminded that the GSoC "soft 
pencils down" milestone approaches, and this is a matter that should be 
resolved before that. I've got two API changes for my stasher package that 
I'd like to receive comments on.

In short, the issues are:

1. What should I name the generalisation of the "apply" subcommand?

2. Parametrised properties: A separate kind of stasher, something the basic 
stasher should support, or a feature that's not needed?

Below is an explanation of issue 1. Issue 2 needs elaborating too (probably 
more than issue 1), but I'll post that in a separate mail later tonight.


1. Replacement for "apply" subcommand.

The v0.3 "apply" subcommand of a stasher uses a computed property as lambda 
in a call to [apply]. Practically, a command prefix

    $S apply

(where $S is a stasher) is equivalent to the command *prefix*

    apply {{S properties value args} {
       set data {}
       foreach p $properties {
          lappend data [$S get $value $p]
       }
       tailcall apply {*}$data {*}$args
    } ::} $S

(A usage example can be something like

    polynomial apply hornerlambda {1 - x + 1/2 x^2 - 1/6 x^3 + 1/24 x^4} 0.3

which ends up making the call

    ::apply {x {expr 
{(((((0)*$x+0.041666666666666664)*$x+-0.16666666666666666)*$x+0.5)*$x+-1)*$x+1}} 
::} 0.3

given the [polynomial] stasher defined in examples/polynomial.tcl file of 
the v0.3.1 stasher distro. Yes, that initial (0)*$x+ is redundant.)

Anyway, it then occurred to me that this is really a special case of a 
slightly more general operation, where instead of ::apply the command uses 
an arbitrary command prefix. Tentatively calling the new subcommand "to", 
one would find that the old

    $STASHER apply

becomes equivalent to

    $STASHER to ::apply

and more generally that the command prefix "$STASHER to" is equivalent to

    apply {{S prefix properties value args} {
       set data {}
       foreach p $properties {
          lappend data [$S get $value $p]
       }
       tailcall {*}$prefix {*}$data {*}$args
    } ::} $STASHER

However, I'm not sure "to" is the most obvious name for this subcommand. 
Maybe "call" would be better? (Both appear as stems in core command names: 
[yieldto] and [tailcall].) Or something else? ("eval" is not available, on 
account of being a separate subcommand.)


Lars Hellström