digitalmars.D.learn - return the other functions of the void main()

Dennis Ritchie (6/6) Apr 09 2015 Hi,

Rikki Cattermole (5/11) Apr 09 2015 Sure when:

John Colvin (2/14) Apr 09 2015 You might wanna check that :p

Rikki Cattermole (4/21) Apr 09 2015 No no, its valid D code. After all, as long as the compiler doesn't

John Colvin (4/26) Apr 09 2015 Ok... not sure how anyone was supposed to know that. The example

Dennis Ritchie (30/38) Apr 09 2015 Thanks.

Jack Applegame (7/34) Apr 09 2015 import std.stdio;

bearophile (4/5) Apr 09 2015 canFind?
Dennis Ritchie (37/80) Apr 09 2015 import std.stdio;

John Colvin (5/11) Apr 09 2015 Yes, because writeln returns nothing, but why would you do that?

"Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> (6/18) Apr 09 2015 It's useful when writing generic wrappers, where you just want to

Dennis Ritchie (56/62) Apr 09 2015 It seems that you can not do so because writeln() something back,

John Colvin (3/66) Apr 09 2015 Try running your code somewhere where you can actually see the

Dennis Ritchie (3/6) Apr 09 2015 Operates a code normally, but still gives the error:

Dennis Ritchie (4/6) Apr 09 2015 I think it has something to do with Vindovs :)

Dennis Ritchie (2/3) Apr 09 2015 *Windows

Ivan Kazmenko (9/12) Apr 10 2015 Indeed, you can test it on Windows locally by running a .cmd file

"Dennis Ritchie" <dennis.ritchie mail.ru> writes:

Hi,
Is it allowed in D similar designs?

void main() {
	import std.stdio;
	return writeln("Hello, world!");
}

Apr 09 2015

Rikki Cattermole <alphaglosined gmail.com> writes:

On 9/04/2015 11:03 p.m., Dennis Ritchie wrote:
 Hi,
 Is it allowed in D similar designs?

 void main() {
      import std.stdio;
      return writeln("Hello, world!");
 }

Sure when:

import std.traits : ReturnType;
import std.stdio : writeln;

static assert(is(ReturnType!writeln == int));

Apr 09 2015

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Thursday, 9 April 2015 at 11:07:05 UTC, Rikki Cattermole wrote:
 On 9/04/2015 11:03 p.m., Dennis Ritchie wrote:
 Hi,
 Is it allowed in D similar designs?

 void main() {
     import std.stdio;
     return writeln("Hello, world!");
 }

 Sure when:

 import std.traits : ReturnType;
 import std.stdio : writeln;

 static assert(is(ReturnType!writeln == int));

You might wanna check that :p

Apr 09 2015

Rikki Cattermole <alphaglosined gmail.com> writes:

On 9/04/2015 11:22 p.m., John Colvin wrote:
 On Thursday, 9 April 2015 at 11:07:05 UTC, Rikki Cattermole wrote:
 On 9/04/2015 11:03 p.m., Dennis Ritchie wrote:
 Hi,
 Is it allowed in D similar designs?

 void main() {
     import std.stdio;
     return writeln("Hello, world!");
 }

 Sure when:

 import std.traits : ReturnType;
 import std.stdio : writeln;

 static assert(is(ReturnType!writeln == int));

 You might wanna check that :p

No no, its valid D code. After all, as long as the compiler doesn't 
assert, its perfectly valid. I was documenting the usage of return for 
main function's when the return type of it is int.

Apr 09 2015

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Thursday, 9 April 2015 at 11:38:26 UTC, Rikki Cattermole wrote:
 On 9/04/2015 11:22 p.m., John Colvin wrote:
 On Thursday, 9 April 2015 at 11:07:05 UTC, Rikki Cattermole 
 wrote:
 On 9/04/2015 11:03 p.m., Dennis Ritchie wrote:
 Hi,
 Is it allowed in D similar designs?

 void main() {
    import std.stdio;
    return writeln("Hello, world!");
 }

 Sure when:

 import std.traits : ReturnType;
 import std.stdio : writeln;

 static assert(is(ReturnType!writeln == int));

 You might wanna check that :p

 I was documenting the usage of return for main function's when 
 the return type of it is int.

Ok... not sure how anyone was supposed to know that. The example 
given used void main. Also, the return type of writeln is void, 
so it's doubly confusing.

Apr 09 2015

"Dennis Ritchie" <dennis.ritchie mail.ru> writes:

On Thursday, 9 April 2015 at 11:07:05 UTC, Rikki Cattermole wrote:
 Sure when:

 import std.traits : ReturnType;
 import std.stdio : writeln;

 static assert(is(ReturnType!writeln == int));

Thanks.

On Thursday, 9 April 2015 at 11:09:43 UTC, John Colvin wrote:
 Yes, because writeln returns nothing, but why would you do 
 that? Just put the return on the next line, it's more readable. 
 Or, in the example above, just omit it entirely as the return 
 is implicit.

I quite often have to write similar designs:

-----
import std.stdio;

void main() {

	auto a = [ 1, 2, 3, 4, 5 ];

	foreach (e; a) {
		if (e == 4) {
			writeln("Yes");
			return;
		}
	}
	
	writeln("No");
}
-----

But is not it easier to write :)

import std.stdio;

void main() {

	auto a = [ 1, 2, 3, 4, 5 ];

	foreach (e; a) {
		if (e == 4) {
			return writeln("Yes");
		}
	}
	
	writeln("No");
}

Apr 09 2015

"Jack Applegame" <japplegame gmail.com> writes:

 I quite often have to write similar designs:

 -----
 import std.stdio;

 void main() {

 	auto a = [ 1, 2, 3, 4, 5 ];

 	foreach (e; a) {
 		if (e == 4) {
 			writeln("Yes");
 			return;
 		}
 	}
 	
 	writeln("No");
 }
 -----

 But is not it easier to write :)

 import std.stdio;

 void main() {

 	auto a = [ 1, 2, 3, 4, 5 ];

 	foreach (e; a) {
 		if (e == 4) {
 			return writeln("Yes");
 		}
 	}
 	
 	writeln("No");
 }

import std.stdio;
import std.algorithm;
import std.array;

void main() {
   auto a = [ 1, 2, 3, 4, 5 ];
   writeln(a.find(4).empty ? "No" : "Yes");
}

Apr 09 2015

"bearophile" <bearophileHUGS lycos.com> writes:

Jack Applegame:

   writeln(a.find(4).empty ? "No" : "Yes");

canFind?

Bye,
bearophile

Apr 09 2015

"Dennis Ritchie" <dennis.ritchie mail.ru> writes:

On Thursday, 9 April 2015 at 12:57:26 UTC, Jack Applegame wrote:
 I quite often have to write similar designs:

 -----
 import std.stdio;

 void main() {

 	auto a = [ 1, 2, 3, 4, 5 ];

 	foreach (e; a) {
 		if (e == 4) {
 			writeln("Yes");
 			return;
 		}
 	}
 	
 	writeln("No");
 }
 -----

 But is not it easier to write :)

 import std.stdio;

 void main() {

 	auto a = [ 1, 2, 3, 4, 5 ];

 	foreach (e; a) {
 		if (e == 4) {
 			return writeln("Yes");
 		}
 	}
 	
 	writeln("No");
 }

 import std.stdio;
 import std.algorithm;
 import std.array;

 void main() {
   auto a = [ 1, 2, 3, 4, 5 ];
   writeln(a.find(4).empty ? "No" : "Yes");
 }

import std.stdio;

void main() {

	foreach (...) {
		foreach (...) {
			...
			if (...) {
				...
				return writeln("Yes");
			}
			...
		}
		...
	}

	...
	
	writeln("No");
}

No design can be completely arbitrary:

-----
import std.stdio;

void main() {

	foreach (...) {
		foreach (...) {
			...
			if (...) {
				...
				return writeln("Yes");
			}
			...
		}
		...
	}

	...
	
	writeln("No");
}

Apr 09 2015

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Thursday, 9 April 2015 at 11:04:00 UTC, Dennis Ritchie wrote:
 Hi,
 Is it allowed in D similar designs?

 void main() {
 	import std.stdio;
 	return writeln("Hello, world!");
 }

Yes, because writeln returns nothing, but why would you do that? 
Just put the return on the next line, it's more readable. Or, in 
the example above, just omit it entirely as the return is 
implicit.

Apr 09 2015

"Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm gmx.net> writes:

On Thursday, 9 April 2015 at 11:09:43 UTC, John Colvin wrote:
 On Thursday, 9 April 2015 at 11:04:00 UTC, Dennis Ritchie wrote:
 Hi,
 Is it allowed in D similar designs?

 void main() {
 	import std.stdio;
 	return writeln("Hello, world!");
 }

 Yes, because writeln returns nothing, but why would you do 
 that? Just put the return on the next line, it's more readable. 
 Or, in the example above, just omit it entirely as the return 
 is implicit.

It's useful when writing generic wrappers, where you just want to 
return whatever the wrapped function returns and don't want to 
treat void functions differently.

I wouldn't use it in normal code, because it can be confusing, as 
`return` usually indicates that a value is indeed returned.

Apr 09 2015

"Dennis Ritchie" <dennis.ritchie mail.ru> writes:

On Thursday, 9 April 2015 at 11:04:00 UTC, Dennis Ritchie wrote:
 Hi,
 Is it allowed in D similar designs?

 void main() {
 	import std.stdio;
 	return writeln("Hello, world!");
 }

It seems that you can not do so because writeln() something back, 
which leads to RUNTIME_ERROR in DMD 2.066.1:

OK:
-----
import std.conv;
import std.stdio;
import std.string;

void main() {
	
	int n = readln.strip.to!int;
	string s = readln.strip;
	
	foreach (from; 0 .. n)
	foreach (jump; 1 .. n) {
		bool ok;
		foreach (i; 0 .. 5) {
			int pos = from + i * jump;
			if (pos >= n || s[pos] != '*') {
				ok = true;
				break;
			}
		}
		if (!ok)
			return write("yes");
	}
	
	write("no");
}
-----
http://codeforces.ru/contest/526/submission/10641745?locale=en

RUNTIME_ERROR:
-----
import std.conv;
import std.stdio;
import std.string;

void main() {

	int n = readln.strip.to!int;
	string s = readln.strip;

	foreach (from; 0 .. n)
		foreach (jump; 1 .. n) {
			bool ok;
			foreach (i; 0 .. 5) {
				int pos = from + i * jump;
				if (pos >= n || s[pos] != '*') {
					ok = true;
					break;
				}
			}
			if (!ok)
				return writeln("yes");
		}

	writeln("no");
}
-----
http://codeforces.ru/contest/526/submission/10641695?locale=en

Apr 09 2015

"John Colvin" <john.loughran.colvin gmail.com> writes:

On Thursday, 9 April 2015 at 16:02:01 UTC, Dennis Ritchie wrote:
 On Thursday, 9 April 2015 at 11:04:00 UTC, Dennis Ritchie wrote:
 Hi,
 Is it allowed in D similar designs?

 void main() {
 	import std.stdio;
 	return writeln("Hello, world!");
 }

 It seems that you can not do so because writeln() something 
 back, which leads to RUNTIME_ERROR in DMD 2.066.1:

 OK:
 -----
 import std.conv;
 import std.stdio;
 import std.string;

 void main() {
 	
 	int n = readln.strip.to!int;
 	string s = readln.strip;
 	
 	foreach (from; 0 .. n)
 	foreach (jump; 1 .. n) {
 		bool ok;
 		foreach (i; 0 .. 5) {
 			int pos = from + i * jump;
 			if (pos >= n || s[pos] != '*') {
 				ok = true;
 				break;
 			}
 		}
 		if (!ok)
 			return write("yes");
 	}
 	
 	write("no");
 }
 -----
 http://codeforces.ru/contest/526/submission/10641745?locale=en

 RUNTIME_ERROR:
 -----
 import std.conv;
 import std.stdio;
 import std.string;

 void main() {

 	int n = readln.strip.to!int;
 	string s = readln.strip;

 	foreach (from; 0 .. n)
 		foreach (jump; 1 .. n) {
 			bool ok;
 			foreach (i; 0 .. 5) {
 				int pos = from + i * jump;
 				if (pos >= n || s[pos] != '*') {
 					ok = true;
 					break;
 				}
 			}
 			if (!ok)
 				return writeln("yes");
 		}

 	writeln("no");
 }
 -----
 http://codeforces.ru/contest/526/submission/10641695?locale=en

Try running your code somewhere where you can actually see the 
output properly. RUNTIME_ERROR isn't something I recognise from D.

Apr 09 2015

"Dennis Ritchie" <dennis.ritchie mail.ru> writes:

On Thursday, 9 April 2015 at 16:55:00 UTC, John Colvin wrote:
 Try running your code somewhere where you can actually see the 
 output properly. RUNTIME_ERROR isn't something I recognise from 
 D.

Operates a code normally, but still gives the error:
http://ideone.com/kDHMk5

Apr 09 2015

"Dennis Ritchie" <dennis.ritchie mail.ru> writes:

On Thursday, 9 April 2015 at 17:08:44 UTC, Dennis Ritchie wrote:
 Operates a code normally, but still gives the error:
 http://ideone.com/kDHMk5

I think it has something to do with Vindovs :)
-----
http://dpaste.dzfl.pl/4c5bb9dd0ffa

Apr 09 2015

"Dennis Ritchie" <dennis.ritchie mail.ru> writes:

On Thursday, 9 April 2015 at 17:38:42 UTC, Dennis Ritchie wrote:
 I think it has something to do with Vindovs :)

*Windows

Apr 09 2015

"Ivan Kazmenko" <gassa mail.ru> writes:

On Thursday, 9 April 2015 at 17:39:43 UTC, Dennis Ritchie wrote:
 On Thursday, 9 April 2015 at 17:38:42 UTC, Dennis Ritchie wrote:
 I think it has something to do with Vindovs :)

 *Windows

Indeed, you can test it on Windows locally by running a .cmd file 
such as:
-----
a.exe
echo %ERRORLEVEL%
-----

With dmd 2.066 (as on Codeforces), it gives me non-zero exit code.

With dmd 2.067.0, the return code seems to always be zero.

Apr 10 2015

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digitalmars.D.learn - return the other functions of the void main()