Why do we have transitive const, again?

[Walter Bright]

On 9/24/2011 6:39 PM, Peter Alexander wrote:
> On 25/09/11 12:08 AM, Walter Bright wrote:
>> 3. support for true functional programming
>
> Purity and (physical) immutability are separate concepts. Having immutable
> arguments is neither a necessary or sufficient condition for being pure.
>
> What do you mean by "true functional programming"? Just pure functional
> programming?
>
> As I explained in my 'Thoughts on Immutability in D' post, physical immutability
> is far too restrictive for functional programming, so I would say that immutable
> in D restricts true functional programming rather than supporting it. Supporting
> functional programming would mean supporting logical immutability, because
> that's all functional programs care about.

Functional programming means (in part) no side effects of functions, which means 
that global state cannot be modified through the parameters. Having the 
parameters be const/immutable is how this can be statically guaranteed.