Re: [TCLCORE] Expr assignment operator

[Neil M. <nei...@gm...>]

If we propose adding := can we at least consider adding it as a statement rather than an operator? I would also prefer if it was a declaration statement rather than assignment. It could even be used to declare new functions, which might make it a bit more interesting. 

Apologies for top-posting. iPhone is my only email access at present. 

Neil

On 22 May 2011, at 09:57, Alexandre Ferrieux <ale...@gm...> wrote:

> On Sun, May 22, 2011 at 9:59 AM, Donal K. Fellows
> <don...@ma...> wrote:
>> 
>> Perhaps we should separate
>> the debate on new RHS operators for lists and dicts from adding
>> assignment (and sequencing, which only makes sense with assignment).
> 
> Right. Changed the subject to dive into the latter.
> 
> Regarding the fact that the assignment operator (let's call it ":=", a
> grey bikeshed will suffice for now) breaks the "single interception
> point" nature of [set], I beg to differ:
> 
> First, [set] is not alone but surrounded with [lappend], [dict
> lappend] etc. So, a sure-fire interception of assignment involves
> exec-tracing many primitives anyway, with a terrible perf impact
> (those assignments being turned from dedicated BC ops into generic
> evalStk calls).
> 
> Second, we could very well introduce [:=] as a kind of "readmacro",
> ie as a preprocessing step on the AST produced by the expr parser,
> replacing (the AST for)
> 
>     LHS:=RHS
> 
> with (the AST for)
> 
>     set LHS [expr {RHS}]
> 
> (or even [set LHS [expr {RHS}]] if we want to allow := in subexprs)
> 
> This would have the effect of:
> 
>    - direct generation of efficient BC (storeScalar/ArrayStk) when
> [set] is not redefined
> 
>    - compile-epoch bumping and traceable generation of a regular call
> to [set] when it is redefined.
> 
> -Alex
> 
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