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digitalmars.D.learn - Pure and higher-order functions

reply "mist" <none none.none> writes:
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 :(
Feb 23 2012
parent reply deadalnix <deadalnix gmail.com> writes:
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).
Feb 23 2012
parent reply "mist" <none none.none> writes:
But is there any way to actually say D compiler that I want this 
function to accept only pure delegates?
Feb 23 2012
parent reply Jonathan M Davis <jmdavisProg gmx.com> writes:
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
Feb 23 2012
parent reply "mist" <none none.none> writes:
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?
Feb 24 2012
parent reply bearophile <bearophileHUGS lycos.com> writes:
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
Feb 24 2012
parent "mist" <none none.none> writes:
Actually, looks like you have done it already 2 years ago :)
http://d.puremagic.com/issues/show_bug.cgi?id=4505
Feb 24 2012