Le 06/08/2012 20:15, Timon Gehr a écrit :
To me, the first big failure of D to implement functional style is to
not have first class functions.
Last time I checked, D still had closures. The 'first big failure of D
to implement functional style' is the lack of most of the other
features traditionally encountered in functional languages.
I mentioned first class function. Functions are not first class, you
have to go throw & .
Actually it is just that function declarations don't introduce symbols
that are bound to values of the first class type.
Try enum foo = (){};
That is what I mean when I say that function are not first class.
&a.foo could be disallowed if foo is bound by UFCS.
It wouldn't be more consistent and would limit expressiveness.
The formalisation can formalise the behaviour in a compatible or mostly
compatible way. eg:
a symbol that refers to a function (template) declaration can appear in
some distinct contexts:
1. its address is taken
2. it is called
3. it is assigned to
4. none of the above
In case 1:
- If the function was looked up by UFCS, then this is the problematic
case. Eg. just error out.
- the address of expression will evaluate to a function pointer
if the function is static and to a suitable delegate otherwise.
In case 2:
- Call.
In case 3:
- Call with the assigned expression.
In case 4:
- Rewrite to a call without parameters.
Why would this be hard to implement?
Well it isn't straightforward, add @property into that and it become
quite scary, now try to keep up with dmd that introduce changes into
that process every release or so and you'll get my point.
Reading the @property thread, it seems that most people want to keep
dmd's current behavior. Because code rely on it. This make sense, but if
dmd's implement is the only goal, it means that other compiler are only
to be reverse engineering dmd's behavior, and are guaranteed to lag
behind. Considering this, I seriously wonder if it make sense to even
try to follow dmd's behavior and decide whatever seems the right one
when writing a D compiler, which will result in community split, or no
alternative compiler produced for D.
I think this is blown out of proportion.
As you say :
That is inevitable if there is only one front end implementation and no
formal specification.
The function call mess is one aspect.
