Elseif v. elsif?


#1

What the?? I just spent two days trying to figure out why I couldn’t
reproduce the example in “Ruby in 20 minutes” and get it to work. After
examining my code line for line against the example code and not being
able to detect any error, I was assembling several code examples into a
text file to post here, when I happened to notice ‘elsif’. Why
didn’t Ruby flag ‘elseif’ as an error?

Does Ruby try differentiate itself in ridiculous ways like that just for
the sake of being different? And why isn’t something like that
explicitly pointed out in a beginning tutorial? So far, I have to give
Ruby two thumbs down.

C++, Java, Javascript, php, Servlets+JSP programmer


#2

On Wed, Mar 07, 2007 at 05:56:56PM +0900, 7stud 7stud wrote:

Does Ruby try differentiate itself in ridiculous ways like that just for
the sake of being different? And why isn’t something like that
explicitly pointed out in a beginning tutorial? So far, I have to give
Ruby two thumbs down.

Ruby isn’t the only language that does that.

“Different” would be more like the way bash does it: “elif”


#3

On 3/7/07, 7stud 7stud removed_email_address@domain.invalid wrote:

What the?? I just spent two days trying to figure out why I couldn’t
reproduce the example in “Ruby in 20 minutes” and get it to work. After
examining my code line for line against the example code and not being
able to detect any error, I was assembling several code examples into a
text file to post here, when I happened to notice ‘elsif’. Why
didn’t Ruby flag ‘elseif’ as an error?
Because it nvere sees it :frowning:

Look at two examples

if true then
whatever
elseif
end

now elsif is seen as an undefined method but

if false then
whatever
elseif
end

whatever and elseif are not evaluated.

I strongly advice you to use a syntax highlighting ediotr like e.g.
vim, emacs, Jedit, geany and tons of others.

Cheers
Robert


#4

On Mar 7, 9:56 am, 7stud 7stud removed_email_address@domain.invalid wrote:

Ruby two thumbs down.

C++, Java, Javascript, php, Servlets+JSP programmer


Posted viahttp://www.ruby-forum.com/.

Well, Ruby doesn’t try to differentiate itself in ridiculous ways just
for the sake of being different. It’s not a person.
However, it will spit out a “undefined method ‘elseif’ for main:Object
(NoMethodError)” when you use ‘elseif’, so it’s really not a problem
is it?


#5

Alle mercoledì 7 marzo 2007, Robert D. ha scritto:

if true then
whatever
elseif
end

now elsif is seen as an undefined method but

Not always. In Robert’s first example,

if true then
whatever
elseif
end

you’ll get a NameError (undefined local variable or method `elseif’ for
main:Object (NameError))

In the following example, instead, you get a syntax error:

if x < 0 then puts “x<0”
elseif x < 3 then puts “0<=x<3”
else puts “x>=3”
end

The error message is:

syntax error, unexpected kTHEN, expecting kEND
elseif x < 3 then puts “0<=x<3”
^
Here, ruby doesn’t complain because elseif doesn’t exist, but because it
finds
a ‘then’ where it shouldn’t be (not following an if or elsif clause). By
the
way, being a syntax error (it when the interpreter is parsing the file,
not
when it executes it), this error is reported whatever the value of x is
(and
even if x doesn’t exist).

All these error messages aren’t very easy to understand for a novice. To
make
a comparison with other programming languages, I tried compiling a C
program
with a similar mistake (in this case writing ‘elseif’ instead of ‘else
if’).
The program was:

int main(){
int a=3;
int b=0;
if( a==4){ b=1;}
elseif(a==2){ b=2;} //should be else if
else{ b=3;}}
}

Compiling with gcc, the error message I got is:

test.c: In function ‘main’:
test.c:5: error: expected ‘;’ before ‘{’ token

As you can see, the error message doesn’t speak of invalid keywords,
but just
of a missing ;

Stefano


#6

Maybe a chapter for that kind of pitfalls could be added somewhere -
well it probably is already, maybe somebody can indicate that.

Perhaps at the “Ruby from other languages” page :
http://www.ruby-lang.org/en/documentation/ruby-from-other-languages/

I find this page very helpful.

Regards,

Chris


#7

On 3/7/07, Hans S. removed_email_address@domain.invalid wrote:

explicitly pointed out in a beginning tutorial? So far, I have to give
(NoMethodError)" when you use ‘elseif’, so it’s really not a problem
is it?


Hans

No of course it is not :slight_smile:
I think to understand the frustration of OP however.
He is probably coming from a completely different world and it is not
always easy to grasp new concepts.
Therefore I preferred to ignore the aggressive nature of the post ;).
He might even have a point when he says that this is maybe not really
well documented, With this I do not mean the “elseif” of course but
just the dynamic evaluation of the code.

Maybe a chapter for that kind of pitfalls could be added somewhere -
well it probably is already, maybe somebody can indicate that.

This is however not a clearcut thing as it might seem at first view.

Robert


#8

My output is:

~/2testing/dir1$ ruby rubyHelloWorld.rb
Hello SallyJaneBob!

ruby version:

~/2testing/dir1$ ruby -v
ruby 1.8.2 (2004-12-25) [universal-darwin8.0]


#9

On 3/7/07, Stefano C. removed_email_address@domain.invalid wrote:

Good points Stefano, conclusion always use “then” :slight_smile:


#10

On Wed, Mar 07, 2007 at 07:54:15PM +0900, 7stud 7stud wrote:

    #functions:
    end

end
if FILE == $0
mg = MegaGreeter.new([“Sally”, “Jane”, “Bob”])
mg.say_hi
end

That’s because you’re not exercising the section under @names.nil?

Try: mg = MegaGreeter.new(nil)


#11

Chris L. wrote:

Maybe a chapter for that kind of pitfalls could be added somewhere -
well it probably is already, maybe somebody can indicate that.

Perhaps at the “Ruby from other languages” page :
http://www.ruby-lang.org/en/documentation/ruby-from-other-languages/

I find this page very helpful.

Regards,

Chris

First, I’d like to say that the web site is really beautiful and eye
catching. There are some minor problems, for instance, the code
examples are in a small area width wise, so there is a horizontal scroll
bar that you need to scroll to the right to see the latter portion of a
line of code. However, the area with the code is very tall(more than
one screen), and it is very inconvenient to page all the way down to the
bottom in order to scroll to the right, and then go all the way back up
in order to read the code. Also, no matter how wide I make my browser
window(Safari 2.0.4), the area with the code does not expand
horizontally. It should expand horizontally as the browser window gets
wider, and the horizontal scroll bars should disappear.

If I run the following code, I don’t get any errors:

class MegaGreeter
attr_accessor :names

    #constructor
    def initialize(names = "world")
            @names = names
    end

    #functions:
    def say_hi
            if @names.nil?
                    puts "..."
            elseif @names.respond_to?("each")
                    @names.each do |name|
                            puts "Hello #{name}!"
                    end
            else
                    puts "Hello #{@names}!"
            end
    end

end
if FILE == $0
mg = MegaGreeter.new([“Sally”, “Jane”, “Bob”])
mg.say_hi
end


#12

On 3/7/07, Brian C. removed_email_address@domain.invalid wrote:

            end

You spoiled it :wink:
but this is a good way to explain it too…


#13

On 3/7/07, 7stud 7stud removed_email_address@domain.invalid wrote:


Posted via http://www.ruby-forum.com/.

I could explain why, but just follow Stefano’s advice and put “then”
after each if elsif and elseif and you will see.

Robert


#14

On Wed, Mar 07, 2007 at 08:05:14PM +0900, Robert D. wrote:

That’s because you’re not exercising the section under @names.nil?

Try: mg = MegaGreeter.new(nil)

You spoiled it :wink:
but this is a good way to explain it too…

and a good argument for code coverage testing (e.g. rcov)


#15

Perhaps at the “Ruby from other languages” page :
http://www.ruby-lang.org/en/documentation/ruby-from-other-languages/

I did a search on the C/C++ page for ‘elsif’ and it wasn’t found.

Ruby isn’t the only language that does that.
“Different” would be more like the way bash does it: “elif”

To me ‘elif’ stands out like a red flag. ‘elsif’ is a more subtle
differentiation, and I couldn’t spot it even though I had the problem
narrowed down to 3 lines of code. The “Ruby in 20 Minutes” tutorial is
obviously geared to the experienced programmer(beginner’s don’t know
what classes are or what an ‘attr_accessor’ is), so I would suggest
putting this in the tutorial:

LOOK AT THE ELSIF SYNTAX CAREFULLY–IT’S ‘ELSIF’ NOT ‘ELSEIF’

with the ‘E’ in elseif in red.


#16

7stud 7stud wrote:

That’s because you’re not exercising the section under @names.nil?
Try: mg = MegaGreeter.new(nil)

You spoiled it :wink:
but this is a good way to explain it too…

What does that have to do with anything?

I tried it, and I got an error for the ‘elseif’. Why is that? If the
first branch succeeds, why is the elsif branch even evaluated?


#17

That’s because you’re not exercising the section under @names.nil?
Try: mg = MegaGreeter.new(nil)

You spoiled it :wink:
but this is a good way to explain it too…

What does that have to do with anything?

Good points Stefano, conclusion always use “then” :slight_smile:

My first exposure to Ruby is the “Ruby in 20 Minutes” tutorial. If it’s
good practice to always use ‘then’, how about putting it in the
tutorial?


#18

7stud 7stud wrote:

7stud 7stud wrote:

That’s because you’re not exercising the section under @names.nil?
Try: mg = MegaGreeter.new(nil)

You spoiled it :wink:
but this is a good way to explain it too…

What does that have to do with anything?

I tried it, and I got an error for the ‘elseif’. Why is that? If the
first branch succeeds, why is the elsif branch even evaluated?

Hmm…I think I get it: Ruby doesn’t realize elseif is another branch,
it just thinks its the next statement after the if statement. But as
far as I know, all if statements are terminated with ‘end’.


#19

On Wed, Mar 07, 2007 at 08:28:43PM +0900, 7stud 7stud wrote:

I tried it, and I got an error for the ‘elseif’. Why is that? If the
first branch succeeds, why is the elsif branch even evaluated?

Hmm…I think I get it: Ruby doesn’t realize elseif is another branch,
it just thinks its the next statement after the if statement. But as
far as I know, all if statements are terminated with ‘end’.

And yours is.

Add some spaces at the front of the ‘elseif’ line, so that it aligns
with
the ‘puts “…”’ on the line above. Then you’ll see how Ruby is
interpreting
your code.

Unlike python, Ruby doesn’t force you to align your source in a
particular
way.


#20

Another question. The tutorial says:

Save this file as “ri20min.rb”, and run it as “ruby ri20min.rb”.

and at the top of the file is the shebang:

#!/usr/bin/env ruby

If you run the program using ‘ruby filename’, do you need the shebang?
I read something that said you only need the shebang if you want to
execute programs using just the filename, e.g.:

$ HelloWorld.rb

also what does ‘env’ do? I read the man pages on the env function, and
I can’t figure out what it does in the shebang.