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digitalmars.D - Select statement?

reply "Lev Elbert" <elbertlev comcast.net> writes:
I have a suggestion: let's include in D a select statement with non-static
conditions:

seclect ()
{
case a < b:
    ....
    break;
case sin(k) < cos(b):
    ....
    break;
case str == "12345":
    ....
    break;
case default:
    ....
    break;
}

which is equivalent to if - else if - else block, but in some cases more
compact and understandable.

I would not mind if instead of select another keyword would be used and
maybe case is not needed.
Regards.
May 19 2004
next sibling parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Lev Elbert wrote:


 I have a suggestion: let's include in D a select statement with non-static
 conditions:
 
 seclect ()
 {
 case a < b:
     ....
     break;




 which is equivalent to if - else if - else block, but in some cases more
 compact and understandable.



Not quite sure how that would be.

if (a < b) {
	....
} else if (sin(k) < cos(b)) {
	....
} else if (str == "12345") {
	....
} else {
	....
}

That's compact.  I'd have no trouble understanding it.  It's even 
cleanly structured compared to switch.

Indeed, I proposed a cleanly structured switch syntax a while back....
D/22722

Stewart.

-- 
My e-mail is valid but not my primary mailbox, aside from its being the 
unfortunate victim of intensive mail-bombing at the moment.  Please keep 
replies on the 'group where everyone may benefit.
May 19 2004
parent reply "Lev Elbert" <elbertlev comcast.net> writes:
Stewart!

if (a < b) {
....
} else if (sin(k) < cos(b)) {
....
} else {
}

isn't a bad substitute for:

select
{
case a < b:                         ..... break;
case (sin(k) < cos(b):       ..... break;
default:                              ..... break;
}

but try to express:

select
{
default:                              ..... break;
case a < b:                         ..... break;
case (sin(k) < cos(b):       ..... break;
}

Based on the results of the discussion bellow, I can tell that most of the
programmers do not need extra expression power. OK! It was just a suggestion
:)

I read your proposal. It is good, but static. "select" covers both static
and non static and optimization is up to compiler.

"Stewart Gordon" <smjg_1998 yahoo.com> wrote in message
news:c8fmuu$20co$1 digitaldaemon.com...

 Lev Elbert wrote:


 I have a suggestion: let's include in D a select statement with







 conditions:

 seclect ()
 {
 case a < b:
     ....
     break;




 which is equivalent to if - else if - else block, but in some cases more
 compact and understandable.



 Not quite sure how that would be.

 if (a < b) {
 ....
 } else if (sin(k) < cos(b)) {
 ....
 } else if (str == "12345") {
 ....
 } else {
 ....
 }

 That's compact.  I'd have no trouble understanding it.  It's even
 cleanly structured compared to switch.

 Indeed, I proposed a cleanly structured switch syntax a while back....
 D/22722

 Stewart.

 --
 My e-mail is valid but not my primary mailbox, aside from its being the
 unfortunate victim of intensive mail-bombing at the moment.  Please keep
 replies on the 'group where everyone may benefit.
May 21 2004
parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Lev Elbert wrote:

<snip>

 but try to express:
 
 select
 {
 default:                     ..... break;
 case a < b:                  ..... break;
 case (sin(k) < cos(b):       ..... break;
 }



What would that achieve?  Besides a little syntax error?


 Based on the results of the discussion bellow, I can tell that most of the
 programmers do not need extra expression power. OK! It was just a suggestion
 :)
 
 I read your proposal. It is good, but static. "select" covers both static
 and non static and optimization is up to compiler.




It is perectly orthogonal to your idea AFAICS.

Stewart.

-- 
My e-mail is valid but not my primary mailbox, aside from its being the 
unfortunate victim of intensive mail-bombing at the moment.  Please keep 
replies on the 'group where everyone may benefit.
May 21 2004
parent reply "Lev Elbert" <elbertlev comcast.net> writes:
 What would that achieve?  Besides a little syntax error?



1. (Sorry for error).
2. In if-else if-else terms: else first. In some cases - more
understandable.

Sure, all what can be expressed by select can be expressed by
if-elseif-else. This is the matter of taste. I just do not like extra
"distracting" words.

In the case

if (...) {
} else if (.....) {
} else {
}

the conditions are hidden in "else ifs".

In short: program with select() would be more compact and understandable
then if-else if.

But discussion is immatereal - nobody wants to implement it :)
May 21 2004
parent reply Stewart Gordon <smjg_1998 yahoo.com> writes:
Lev Elbert wrote:

What would that achieve?  Besides a little syntax error?



 
 1. (Sorry for error).
 2. In if-else if-else terms: else first. In some cases - more
 understandable.



What order of checking would the rest of the terms have?  Start at the 
bottom and work up?

<snip>

 In short: program with select() would be more compact and understandable
 then if-else if.




More compact?

select {
	case ...:
		...
		break;
	case ...:
		...
		break;
	default:
		...
}

versus

if (...) {
	...
} else if (...) {
	...
} else {
	...
}

OTOH, if my suggested syntax is extended to this, we'd have

select {
	case ... {
		...
	} else case ... {
		...
	} else {
		...
	}
}

                        if    select/break  block select
Lines (as shown)        7    10             9
Tokens                 14    13            13
Chars (as shown)       39    63            57
Chars (squashed up)    23    31            38

(The token and char counts exclude the dots.)

OK, so it saves a token in this example, but that's about all it saves. 
  As for more understandable, maybe.  But as you rightly say, it's a 
matter of style.

Stewart.

-- 
My e-mail is valid but not my primary mailbox, aside from its being the 
unfortunate victim of intensive mail-bombing at the moment.  Please keep 
replies on the 'group where everyone may benefit.
May 24 2004
parent reply Mike Swieton <mike swieton.net> writes:
On Mon, 24 May 2004 10:43:11 +0100, Stewart Gordon wrote:


 OTOH, if my suggested syntax is extended to this, we'd have
 
 select {
 	case ... {
 		...
 	} else case ... {
 		...
 	} else {
 		...
 	}
 }
 
                         if    select/break  block select
 Lines (as shown)        7    10             9
 Tokens                 14    13            13
 Chars (as shown)       39    63            57
 Chars (squashed up)    23    31            38
 
 (The token and char counts exclude the dots.)
 
 OK, so it saves a token in this example, but that's about all it saves. 
   As for more understandable, maybe.  But as you rightly say, it's a 
 matter of style.
 
 Stewart.



I dislike your style blocks because:
	- it appears that they would make case fallthrough be confusing or
		impossible.
	- they differ from existing standards, and I don't feel they add enough to
		justify the difference.
	- a change would break existing code.

I don't think the advantages outweight the disadvantages.

Mike Swieton
__
It's so simple to be wise. Just think of something stupid to say and then
don't say it.
	- Sam Levenson
May 24 2004
next sibling parent reply J Anderson <REMOVEanderson badmama.com.au> writes:
Mike Swieton wrote:


On Mon, 24 May 2004 10:43:11 +0100, Stewart Gordon wrote:

  


OTOH, if my suggested syntax is extended to this, we'd have

select {
	case ... {
		...
	} else case ... {
		...
	} else {
		...
	}
}

                        if    select/break  block select
Lines (as shown)        7    10             9
Tokens                 14    13            13
Chars (as shown)       39    63            57
Chars (squashed up)    23    31            38

(The token and char counts exclude the dots.)

OK, so it saves a token in this example, but that's about all it saves. 
  As for more understandable, maybe.  But as you rightly say, it's a 
matter of style.

Stewart.
    



I dislike your style blocks because:
	- it appears that they would make case fallthrough be confusing or
		impossible.
	- they differ from existing standards, and I don't feel they add enough to
		justify the difference.
	- a change would break existing code.
  



there's a need for the else part.  Something like:

switch (...)
{
case ...
{

}
case ...
{

}
}

Fall through is a big problem for many programmers.

-- 
-Anderson: http://badmama.com.au/~anderson/
May 24 2004
parent Stewart Gordon <smjg_1998 yahoo.com> writes:
J Anderson wrote:

<snip>

 Also I don't think there's a need for the else part.  Something like:
 
 switch (...)
 {
 case ...
 {
 
 }
 case ...
 {
 
 }
 }




That would cause the second part to be executed if its case matched, 
even if the first case also matched.

Of course, in the one I gave, the final else could otherwise be default.

Stewart.

-- 
My e-mail is valid but not my primary mailbox, aside from its being the 
unfortunate victim of intensive mail-bombing at the moment.  Please keep 
replies on the 'group where everyone may benefit.
May 25 2004
prev sibling parent Stewart Gordon <smjg_1998 yahoo.com> writes:
Mike Swieton wrote:

<snip>

 I dislike your style blocks because:
 	- it appears that they would make case fallthrough be confusing or
 		impossible.



Confusing - not sure.

Impossible - only if the condition has a side effect.  Otherwise, you 
can do it by nesting cases.

Of course, you would need to repeat the condition to be fallen through 
from, but considering that fall-through is a bit of a dirty trick anyway....


 	- they differ from existing standards, and I don't feel they add enough to
 		justify the difference.



No more than the very invention of a select statement would in the first 
place.  If a specification were set in so much stone that it couldn't 
even be added to, you wouldn't


 	- a change would break existing code.



How?

Stewart.

-- 
My e-mail is valid but not my primary mailbox, aside from its being the 
unfortunate victim of intensive mail-bombing at the moment.  Please keep 
replies on the 'group where everyone may benefit.
May 25 2004
prev sibling next sibling parent Andy Friesen <andy ikagames.com> writes:
Lev Elbert wrote:

 I have a suggestion: let's include in D a select statement with non-static
 conditions:
 
 which is equivalent to if - else if - else block, but in some cases more
 compact and understandable.
 
 I would not mind if instead of select another keyword would be used and
 maybe case is not needed.
 Regards.



There's not much point in this because it doesn't really affect what D 
can express, nor does it save a huge amount of effort when one is trying 
to express any particular idea.

  -- andy
May 19 2004
prev sibling parent reply h3r3tic <h3r3tic_member pathlink.com> writes:
In article <c8fk6j$1s53$1 digitaldaemon.com>, Lev Elbert says...

seclect ()
{
case a < b:
    ....
    break;
case sin(k) < cos(b):
    ....
    break;
 (...)

which is equivalent to if - else if - else block, but in some cases more
compact and understandable.




or just add 'elif' for lazy ppl :P
May 19 2004
parent reply Juan C <Juan_member pathlink.com> writes:
or just add 'elif' for lazy ppl :P



Lazy is right, I never saw any need for elif;  "else if"  works just fine, is
easier to read, etc. etc. etc...
May 19 2004
parent reply Roel Mathys <roel.mathys yucom.be> writes:
Juan C wrote:


or just add 'elif' for lazy ppl :P



 
 Lazy is right, I never saw any need for elif;  "else if"  works just fine, is
 easier to read, etc. etc. etc...
 
 



yeah, but elif is 4 letters, else if is 6 letters and a space, that's 
upto 75% more, so adding elif would mean an increase in productivity of 
almost 43%

:-)

roel
May 19 2004
parent reply Juan C <Juan_member pathlink.com> writes:
yeah, but elif is 4 letters, else if is 6 letters and a space, that's 
upto 75% more, so adding elif would mean an increase in productivity of 
almost 43%



Well, no, a disk storage (and network transfer) savings of 43%. And I've only
got 75GB of free space on my disk! I'd better watch out.

One of my Perl books around here states (jokingly I hope) that Perl doesn't have
"elif" because it's "file" spelled backward. Who am I to argue with that?  (Oy!)

More seriously: if "elif" is added simply to take the place of "else if", I
would hope that "else if" becomes illegal. On the other hand you can write
"elif" and have a text replacement utility replace it with "else if".
May 19 2004
next sibling parent reply Roel Mathys <roel.mathys yucom.be> writes:
Juan C wrote:


yeah, but elif is 4 letters, else if is 6 letters and a space, that's 
upto 75% more, so adding elif would mean an increase in productivity of 
almost 43%



 
 Well, no, a disk storage (and network transfer) savings of 43%. And I've only
 got 75GB of free space on my disk! I'd better watch out.
 
 One of my Perl books around here states (jokingly I hope) that Perl doesn't
have
 "elif" because it's "file" spelled backward. Who am I to argue with that? 
(Oy!)
 
 More seriously: if "elif" is added simply to take the place of "else if", I
 would hope that "else if" becomes illegal. On the other hand you can write
 "elif" and have a text replacement utility replace it with "else if".
 
 



this could be "the" ultimate reason to add a preprocessor to D,
replace all "elif" with "else if" <g>

bye,
roel
May 19 2004
next sibling parent reply Juan C <Juan_member pathlink.com> writes:
this could be "the" ultimate reason to add a preprocessor to D,
replace all "elif" with "else if" <g>



Not a full-blown preprocessor, just a simple one. Or allow "C preprocessor"
output to be piped into the compiler, of course that's up to the compiler
writer, not the language.

If there were several competing D compilers (and there will be) features like
this could be deciding factors in choosing one. (Can you say "non-portable"?)

Barring that, the community ought to agree on one text replacement utility to
use. And if that were the C preprocessor it would be abused I'm sure.

Oh, I keep forgetting to see if I could use HTML for text replacement!
May 19 2004
parent Roel Mathys <roel.mathys yucom.be> writes:
Juan C wrote:


 If there were several competing D compilers (and there will be) features like
 this could be deciding factors in choosing one. (Can you say "non-portable"?)



I don't agree, I've seen enough so-called 4th generation language tools, 
this would be one more.

code containing the elif is not D, as long as the specification does not 
allow it. It's best to put in the specs (before 1.0 is released) how 
vendor-specific extension can be but into the language.
C++ has something like that, don't recall exactly what it is, but MS 
used it to define some extra's into their Managed C++.

bye,
roel
May 20 2004
prev sibling next sibling parent James McComb <alan jamesmccomb.id.au> writes:
Roel Mathys wrote:


 this could be "the" ultimate reason to add a preprocessor to D,
 replace all "elif" with "else if" <g>



Yeah, Walter, let's see your fancy mixins do this! ;)

James McComb
May 19 2004
prev sibling parent Ant <duitoolkit yahoo.ca> writes:
On Wed, 19 May 2004 23:19:26 +0200, Roel Mathys wrote:


 Juan C wrote:
 

yeah, but elif is 4 letters, else if is 6 letters and a space, that's 
upto 75% more, so adding elif would mean an increase in productivity of 
almost 43%



 
 Well, no, a disk storage (and network transfer) savings of 43%. And I've only
 got 75GB of free space on my disk! I'd better watch out.
 
 One of my Perl books around here states (jokingly I hope) that Perl doesn't
have
 "elif" because it's "file" spelled backward. Who am I to argue with that? 
(Oy!)
 
 More seriously: if "elif" is added simply to take the place of "else if", I
 would hope that "else if" becomes illegal. On the other hand you can write
 "elif" and have a text replacement utility replace it with "else if".
 
 



 this could be "the" ultimate reason to add a preprocessor to D,
 replace all "elif" with "else if" <g>
 



No this is the job of your IDE.

in leds you can define any identifier to expande to any text
you can have gpl expanded to the gpl common header with the project
name inserted.
you can define "ei" to expande to"

if ( $cursor )
{
}
else if (  )
{
}
else
{
}

any minimal code editor should be able to do that.

Ant
May 19 2004
prev sibling parent Stewart Gordon <smjg_1998 yahoo.com> writes:
Juan C wrote:

 yeah, but elif is 4 letters, else if is 6 letters and a space,
 that's upto 75% more, so adding elif would mean an increase in
 productivity of almost 43%



 Well, no, a disk storage (and network transfer) savings of 43%. And
 I've only got 75GB of free space on my disk! I'd better watch out.



As if

	else ifelse ifelse ifelse ifelse ifelse ifelse ifelse ifelse if

were a valid program....


 One of my Perl books around here states (jokingly I hope) that Perl
 doesn't have "elif" because it's "file" spelled backward. Who am I to
 argue with that?  (Oy!)



Maybe you should use lreP then....


 More seriously: if "elif" is added simply to take the place of "else
 if", I would hope that "else if" becomes illegal.



What would that achieve?


 On the other hand you can write "elif" and have a text replacement
 utility replace it with "else if".



You could do all kinds of text replacements to translate an ad-hoc 
language into D.

Stewart.

-- 
My e-mail is valid but not my primary mailbox, aside from its being the
unfortunate victim of intensive mail-bombing at the moment.  Please keep
replies on the 'group where everyone may benefit.
May 20 2004