OpenEuphoria

1. foreach

• Posted by ryanj Jul 23, 2008
• 1033 views

I think euphoria 4.0 should have a foreach block.

Example:

foreach x in s do 
    puts(1, x) 
end foreach 
 
--vs 
for x = 1 to length(s) do 
    puts(1, s[x]) 
end for 

Ryan J.

3. Re: foreach

• Posted by SDPringle Jul 23, 2008
• 1017 views
• Last edited Jul 24, 2008

Why don't you guys release 4.0 with out adding features then add all these features in 4.1. Let the public pound on what you have finished so far.

Shawn Pringle

5. Re: foreach

• Posted by jeremy (admin) Jul 23, 2008
• 1015 views
• Last edited Jul 24, 2008

While we are talking about foreach, maybe we should just hash it out? I am not sure of syntax issues, the foreach given by ryan is pretty standard?

Jeremy

7. Re: foreach

• Posted by eumario Jul 23, 2008
• 1049 views
• Last edited Jul 24, 2008

Jeremy is correct in this. I know that Ruby started development back around this time last year on 1.9.0, and didn't make an official release till December of 2007. And it still isn't at an official release. Python hit 3.0 alpha around August 2007, and they are just finally reaching the Beta phase.

While you may be anxious, what these guys have done, has been an utter miracle to bring the Interpreter as far as they have. And there's still a lot of work to be done, if you want to believe it or not. Work on the Interpreter to get everything correct, is strongly needed, especially to bring Euphoria up to compete with other languages, as far as Keyword features that are available in the language.

So sit back, relax, and enjoy the ride. If your so anxious, see about checking out the eubins (http://jeremy.cowgar.com/eubins/) and use SVN to check out the code. That is what I've been doing, and I'm perfectly happy with it, cause it gives me a chance to test for bugs, and let the others know what I find, so that they can work on it, and get it out there faster.

L8ers,

9. Re: foreach

• Posted by CChris Jul 24, 2008
• 1014 views

I wouldn't call most of the below "issues", but obviously expected stuff. This is why I was confused by the mention of syntax issues.

[/quote]

foreach x in s do 
    if x > n then 
       x /= 2 
    end if 
end for 

for x = 1 to length(s) do 
    if s[x] > n then 
       s[x] /= 2 
    end if 
end for 

Since x is not an index variable, it doesn't need to be read only. Why mixing things up?

foreach x[i] in s do 
    if i > 1 then 
      if x > s[i-1] then 
       x /= 2 
      end if 
    end if 
end for 

I think I'd find

foreach x in s index i do 

clearer, but wouldn't mind. The index clause woould be optional, and the foreach loop index would be read only.

foreach x in s, y in t do 
  if x > y then 
     x = y 
  end if 
end for 

I would say yes, but what happens when s and t have different lengths? I would quit whenever any parallelly processed sequence is exhausted. Also, the extra comma is not usual in Eu, can be removed.

foreach x in reversed s do 
  if find(x, " \t\r\n") = 0 then 
    exit 
  end if 
  x = ' ' 
end for 

Why not?

foreach x in s do 
  if x > 1 then 
     s = func(s) 
  end if 
end for 

This is the only item I'd consider an issue.

My understanding would be this: foreach dumbly traverses the sequence, one element after the previous/next, and quits when no more is found. This behaviour is, I think, the only one we can implement efficiently, and it may be the desired thing in some cases. It won't be always so, but then why not use a while loop? I assume these will be uncommon enough cases.

Dynamic s-es will be handled much more efficiently than having to test always for valid indexes - the interpreter does it anyway, so that's duplicated code.

Even though I'd definitel use foreach it it was there, it can wait past 4.0 alpha, as it does not modify current code. Except for variables/routines currently named "foreach", of course.

Actually, there is another issue which could be raised, and which is common to for loops: should the scope for the index variable be extended? And should the object variable in the foreach construct be scoped inside the foreach loop proper? But this is a connected issue for another thread.

CChris

11. Re: foreach

• Posted by SDPringle Jul 24, 2008
• 1032 views

What about the ability to edit the list itself?

What happens when you do something like: s = repeat(0,10) for i = 1 to length(s) do s = s[1..$-1] ? i end for

or

for i = 1 to length(s) do s = s[1..$-1] ? i end for

or

foreach value in s do ? value s = s[1..$-1] end foreach

I have had problems doing this kind of thing in the past. I cannot tell you what because it has been so long ago and I convert them to while loops when ever I want to increment the index manually or modify the list in anyway.

P.S.: Quote Reply seems broken now.

13. Re: foreach

• Posted by unkmar Jul 24, 2008
• 1022 views

s = {1,2,3} 
 
foreach x in s do 
    x *= 2 
end foreach 
 
-- s is now {2, 4, 6} 

s = {1, 2, 3} 
foreach x in s do 
    ? x 
end foreach 
 
-- Same as: 
 
for i = 1 to length(s) do 
    x = s[i] 
    ? x 
end for 

This view fits very well within my expectations of an intial version. I agree that additional features should only be added after the 4.0 release. Allowing everyone plenty of time to hash out their opinions on the positives and negatives of each nuance.

Another optional format is:

--parentheses are optional.  Just part of my coding style. 
-- I don't like this format 
foreach (list as item) do 
  ? item 
end foreach 
 
--I prefer this 
foreach (item in list) do 
  ? item 
end foreach 

15. Re: foreach

• Posted by CChris Jul 24, 2008
• 1011 views

s = {1,2,3} 
foreach x in s do 
    ? x 
end foreach 
 
-- being identical to: 
 
s = {1,2,3} 
for i = 1 to length(s) do 
    object x = s[i] 
    ? x 
end for 

Or 4.0 beta.

It all depends of the time frame. More time, moreextra possible twists and tweaks.

CChris

17. Re: foreach

• Posted by mattlewis (admin) Jul 24, 2008
• 1028 views

It can only be safely done if, in 4.0, x is treated like a for loop variable currently is (i.e., no assignment possible).

And to lump something else in there, what about [optionally] specifying a type for the 'each'?

foreach integer c in my_string do 
    -- ... 
end foreach 

Matt

19. Re: foreach

• Posted by DerekParnell (admin) Jul 24, 2008
• 1033 views

foreach integer c in my_string do 
    -- ... 
end foreach 

What is the semantics behind that?

Does it mean that it only selects the integers contained in my_string and ignores non-integers? Or does it crash if a non-integer is found?

21. Re: foreach

• Posted by DerekParnell (admin) Jul 24, 2008
• 997 views

foreach integer c in my_string do 
    -- ... 
end foreach 

for i = 1 to length(my_string) do 
    integer c = my_string[i] 
    -- ... 
end for 

Ok. However keep in mind that I'll be proposing a 4.x modification to the for family of statements that would allow declaring the loop variable outside the actual for statement so it can have a wider scope.

Something like ...

integer c 
for defined c = 1 to 10 do 
    if func(c) then exit end if 
end for 
printf(1, "The value of 'c' is %d\n", c) 

23. Re: foreach

• Posted by unkmar Jul 24, 2008
• 999 views
• Last edited Jul 25, 2008

integer c 
for defined c = 1 to 10 do 
    if func(c) then exit end if 
end for 
printf(1, "The value of 'c' is %d\n", c) 

I'm good with that as long as the following still crashes with an error.

integer varCT, varEbull 
for varCT = 1 to 10 do 
  for varEbull = 1 to 10 do 
    for varCT = 1 to 10 do -- Attempt to reuse active for loop variable 'varCT' 
    end for 
  end for 
end for 
--Just thought I would use something stranger than foo and bar.  
--Sound them out. 

25. Re: foreach

• Posted by CChris Jul 25, 2008
• 978 views

Matt said:

While I certainly see the utility in this, the more I think about it, it's not a very euphorian concept. Everywhere else in the language, we have assignment by value, and then here we have something operating by reference. So not something to be done lightly, I think...

Matt [/quote]

But doesn't that highlight the fact that what is natural for VB is not so natural for Euphoria. In VB, when using foreach to iterate through a collection of objects, you can access the object by index or name via object methods. Transposing this to Euphoria, you get a reference alias 'x' that gives you no access to its index and unnatural access to the real variable - even more unnatural if the real variable doesn't exist at all because it is the reverse of a real variable (or alternatively, a slice of one, like s[1..4] ).

Surely in Euphoria, you want to reference the elements by index, not by reference, something like this:-

foreach index in s do 
 
   if index < 3 then 
      s[index] += 1 
   else 
      s[index] += 2 
   end if 
 
end for 

This allows you to access both the sequence element directly and its index, whichever is you want. To me, the reference variable seems completely superfluous.

Cheers Peter

[/quote]

Euphoria may some day become an adult language, and among other things will have some pass by ref mechanism. The sooner it gets into the language the better.

But in the meantime, I find your syntax very confusing, because a sequence is made of elements, not of indexes. I think I'd prefer then:

foreach s[index] do 
-- whatever 
end foreach --<-- when do we get rid of that redundancy? 

Whether index is read only is an issue - I think it shouldn't, but don't really care -. And s[index] would be available for either read or write.

CChris

27. Re: foreach

• Posted by mattlewis (admin) Jul 25, 2008
• 972 views

foreach s[index] do 
-- whatever 
end foreach --<-- when do we get rid of that redundancy? 

It doesn't need it, but it uses it to make sure that it understands what we're trying to tell it. Much easier than C or Java, where you have to track back to figure out where you missed or added a curly bracket.

Matt

29. Re: foreach

• Posted by SDPringle Jul 29, 2008
• 949 views

Pass by reference isn't a difficult problem for me to use in other languages but you know its rather EUPHORIA's character to show you pass by value semantics even though it would have been easier for the EUPHORIA's implementor to give you pass by reference semantics. I don't think because a language does away with a concept such as manual pass by ref that it should be called not yet adult language.

Exclusive pass by value gives you the debugging advantage to know that the only things that get modified in some scope are on the left side of an equals sign (and not some where in the scope of a called routine). Yet, it actually sends only the pointer instead of a memcpy as so many C programmers imagine when I tell them about it. So, it must decide to do the copy if you write to a passed value. You can call this copy-on-write-pass-by-value (COWPBV).

Does foreach break this concept though?

Assigning to a foreach variable is similiar to assigning to a sequence member indexed with a for loop.

I propose for the reversed syntax you could have reverse(s). Instead of actually doing a reverse function call the loop would transverse s in a reversed fashion. To the programmer it behaves the same as though you were reversing first and going through in a foward manner, yet it is faster. It is analogous to COWPBV it simplifies semantics for you, yet gives you a fast implementation.

Shawn Pringle