Re: Pure and higher-order functions

2012-02-24 Thread mist 

Ok, finally understood.

I was trying to declare hof like this: void f2( pure int 
function() param ) , similar to the way I declare usual pure 
functions. Looks like it is syntax error and only void f2( int 
function() pure param ) is allowed. That led me to false 
conclusion, that such signature is not allowed at all.


Are there any reasons for this inconsistency?

Re: Pure and higher-order functions

2012-02-24 Thread bearophile 
mist:

 Are there any reasons for this inconsistency?

I don't know. Maybe it's just a parser bug. There are some of those in Bugzilla.

If you don't like it, then I suggest you to add it to D Bugzilla.

Bye,
bearophile

Re: Pure and higher-order functions

2012-02-24 Thread mist 

Actually, looks like you have done it already 2 years ago :)
http://d.puremagic.com/issues/show_bug.cgi?id=4505

Re: Pure and higher-order functions

2012-02-23 Thread deadalnix 

Le 23/02/2012 21:00, mist a écrit :

Hello!

I have been asked few question recently from a Haskell programmer about
D2 and, after experimenting a bit, have found that I really can't
provide a good answe myself, as I am not getting a design limititations
(if any).

Here is the snippet, it is pretty self-descriptive:
http://codepad.org/DBdCJYI2

Am i right, that all information about purity  Co is lost at runtime
and there is no way to write pure-aware higher-order function using
dynamic function pointers? That would have made me really sad :(


Information is lost because of what f2 accept as a type. f2'q param 
isn't pure, so you gat what you except.


Within f2, the fact that your function is pure is lost. f2 accept any 
function, pure or not.


pure function can be casted automatically to non pure, because it is 
safe, but the other way around, it is impossible (because purity 
constraint would be broken).

Re: Pure and higher-order functions

2012-02-23 Thread mist 
But is there any way to actually say D compiler that I want this 
function to accept only pure delegates?

Re: Pure and higher-order functions

2012-02-23 Thread Jonathan M Davis 
On Thursday, February 23, 2012 21:17:46 mist wrote:
 But is there any way to actually say D compiler that I want this
 function to accept only pure delegates?

Mark the delegate type that it accepts as pure.

- Jonathan M Davis