1. Re: we need official libs : Swap
Hello,
Boehme, Gabriel wrote:
<lots of good stuff and this>
>1) The receiving structure may *not* contain duplicate variables.
>
> a) Duplicate variable names would be caught *before* execution.
>
> Example:
> {a,b} = {1,2} -- legal
> {a,a} = {1,2} -- error!
>
> b) Duplicate variable subscripts would be caught at run time.
> (This would probably be the most difficult condition to verify.)
>
> Examples:
> {a[7], a[9]} = {1,2} -- legal
> {a[7], a[7]} = {1,2} -- error!
> {a[7][2], a[7]} = {1,2} -- NASTY error!
> {a[x], a[y]} = {1,2} -- legal only if x != y
> {a[x][z], a[y]} = {1,2} -- legal only if x != y
> {a[7], a[9]} = {a[9], a[7]} -- legal, swaps the variables
> {a[x], a[y]} = {a[y], a[x]} -- legal only if x != y
> -- (if they're equal, then
> -- it's redundant anyway...)
> {a[x][z], a[y]} = {a[y], a[x][z]} -- legal, swaps the variables
> -- but *only* if x != y
> -- (my, we're *really* opening
> -- a can of worms here...)
>
>2) If the expression returns a sequence value, then its structure must
> match the specified receiving structure *exactly*.
>
> Examples:
> {a,b} = {1,2} -- legal
> {a,b} = {1,2,3} -- error!
> {a,{b,c}} = {1,{2,3}} -- legal
> {a,{b,c}} = {1,{2,3,4}} -- error!
> {a,b} = {b,a} -- legal, swaps the variables
> {a,b} = {b,b} -- legal, but a bit redundant
> {b,b} = {a,b} -- error! (see #1 above)
>
>3) If the expression returns an atom value, this value will be applied to
> *all* receiving variables. (NOTE: I'm not 100% sure about this idea,
>but
> it *does* fit with the s[i..j] = 0 method of slice assignment...)
>
> Examples:
> {a,b} = 2 -- legal
> {a,{b,c}} = 2 -- legal, but unnecessarily complicated
> {a,b,c} = 2 -- legal, identical to the above
>
>4) Every received value *must* be assigned to its own variable, i.e.
> no "placeholder" symbols, no repeated "junk" values (see #1 above).
>
> Example:
> {_, keep, _} = {1,2,3} -- error! "_" is not a variable
> {junk, keep, junk} = {1,2,3} -- error! "junk" is repeated
> {junk1, keep, junk2} = {1,2,3} -- legal, though not elegant
>
<SNIP>
>Nevertheless, it does appear to me that this idea *can* be made into a
>reasonably clear and self-consistent part of Euphoria; and, certainly, this
>is the kind of thinking which *must* be done if we want to make this an
>integrated part of the language.
Thank you Gabriel for doing us the favor of extensively
defining the rules that could govern this sort of addition
to Euphoria. I like these rules and hope that this addition
will be made. I want to mention that I still think that the
{a, b} = <EXPRESSION> idea is Euphoric, consistent, and
clear. I'm dying to know if Robert will considder adding
this to a future release.
TIA,
Lewis Townsend
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