• Michiel (11/11) Feb 13 2007 I was thinking it might be useful if you could create custom control flo...
• Mikola Lysenko (18/36) Feb 13 2007 To an extent, this is already possible. DCSP does this for stuff like
• Michiel (4/17) Feb 13 2007 I think the semicolon would be in the way. I don't think this syntactic ...
• Mikola Lysenko (9/24) Feb 13 2007 No, you're absolutely right. My mistake about the semicolon.
• Michiel (5/12) Feb 13 2007 I tried this: writefln("foo", writefln("bar"));

Michiel <nomail hotmail.com> writes:

I was thinking it might be useful if you could create custom control flow
statements like:

foreach_random (element, array) { ... }

Might just be an idea for the future of D. It could be declared like this:

void foreach_random(T)(T element, T[] array, void delegate() statements) { ... }

It would work kind of like those array functions, where the first array
parameter can also be placed in front of the function with a . inbetween. In
this case the last delegate parameter can also be placed after (without a .).

In theory you could also create things like:

threeway (x, 3) { ... } { ... } { ... }

What do you think?

Mikola Lysenko <mclysenk mtu.edu> writes:

Michiel wrote:
 I was thinking it might be useful if you could create custom control flow
 statements like:
 
 foreach_random (element, array) { ... }
 
 Might just be an idea for the future of D. It could be declared like this:
 
 void foreach_random(T)(T element, T[] array, void delegate() statements) { ...
}
 
 It would work kind of like those array functions, where the first array
 parameter can also be placed in front of the function with a . inbetween. In
 this case the last delegate parameter can also be placed after (without a .).
 
 In theory you could also create things like:
 
 threeway (x, 3) { ... } { ... } { ... }
 
 What do you think?

To an extent, this is already possible.  DCSP does this for stuff like 
parallel code blocks and alternative statements.

http://assertfalse.com

However, any syntactic sugar like this needs to be very carefully 
thought out.  Consider the following:

void a()
{
	writefln("starting");

	{
		scope(exit) writefln("blah");
	}
}

This is valid code and there are many times where something like this is 
needed.  Unfortunately, if we implement what you suggest, then the 
second block would get convereted to a delegate and passed as a variadic 
argument to writefln!

-Mik

Michiel <nomail hotmail.com> writes:

 However, any syntactic sugar like this needs to be very carefully
 thought out.  Consider the following:

 void a()
 {
  writefln("starting");

  {
   scope(exit) writefln("blah");
  }
 }

 This is valid code and there are many times where something like this is
 needed.  Unfortunately, if we implement what you suggest, then the
 second block would get convereted to a delegate and passed as a variadic
 argument to writefln!

I think the semicolon would be in the way. I don't think this syntactic sugar is
in conflict with any existing syntax. You can never create a function with the
name 'scope' or 'for' or 'if', so there's no problem there either.

Or am I missing something?

Mikola Lysenko <mclysenk mtu.edu> writes:

Michiel wrote:
 void a()
 {
  writefln("starting");

  {
   scope(exit) writefln("blah");
  }
 }

 
 I think the semicolon would be in the way. I don't think this syntactic sugar
is
 in conflict with any existing syntax. You can never create a function with the
 name 'scope' or 'for' or 'if', so there's no problem there either.
 
 Or am I missing something?

No, you're absolutely right.  My mistake about the semicolon.


I guess my main concern is what happens when semicolon typos occur.  If 
something like this is valid:

if(true)
	writefln("foo");

Would the same logic apply in situations like:

writefln("foo")
writefln("bar");

Michiel <nomail hotmail.com> writes:

 I guess my main concern is what happens when semicolon typos occur.  If
 something like this is valid:

 if(true)
  writefln("foo");

 Would the same logic apply in situations like:

 writefln("foo")
 writefln("bar");

I tried this: writefln("foo", writefln("bar"));

It gives a compiler error. So it may be a bad example. But you do have a point.
Maybe a special keyword should be used to tell the compiler you want the special
behavior. Like:

void functionName(int param1, loose void delegate() statements) { ... }