On 25/09/11 2:52 AM, Walter Bright wrote:
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.
It's easy to guarantee something. The difficult part is guaranteeing
something without overly restricting it.
You could just as easily get the same guarantee by disallowing
references and forcing people to copy data across threads all the time.
That would be a terrible. Likewise, getting the guarantee by forbidding
equality preserving mutations is also terrible, although to a lesser extent.
