So surprised syntax error not caught here

Ruby
1

the following syntax error for “elif” is not caught? (should be elsif)

def foo(i)
if i < 0
return “Less than 0”
elif i == 0
return “it is zero”
else
return “Greater than 0”
end
end

p foo(-2)
p foo(0)
p foo(10)

==================
Output:

“Less than 0”
“Greater than 0”
“Greater than 0”

2

From: [email protected] [mailto:[email protected]] On Behalf
Of
SpringFlowers AutumnMoon
Sent: Tuesday, September 25, 2007 7:50 PM

end
end

Rewrite indents this way to understand:

def foo(i)
if i < 0
return “Less than 0”
elif i == 0
return “it is zero”
else
return “Greater than 0”
end
end

The “problem line” is parsed as

elif(i == 0)

Interpreter doesn’t complain on non-existent “elif” methods, because the
line just never evaluated.

V.

3

On 9/25/07, SpringFlowers AutumnMoon [email protected] wrote:

end

p foo(-2)
p foo(0)
p foo(10)

It’s treating “elif” as a (possible) method call that’s never reached
because of the “return”. You don’t need “return” for what you have:

def foo(i)
if i < 0
“Less than 0”
elif i.zero? # i == 0
“Equal to 0”
else
“Greater than 0”
end
end

That will fail, but not with a syntax error. (It should fail with an
UnknownMethod.) Ruby is expression-oriented, and the last expression
executed in the execution path is returned from the execution path.

-austin

4

SpringFlowers AutumnMoon wrote:

the following syntax error for “elif” is not caught? (should be elsif)

def foo(i)
if i < 0
return “Less than 0”
elif i == 0
return “it is zero”

Ruby is interpretive; it does not link all its symbols to real
entities at compile time. (Unlike certain other languages we could
mention.

elif could be a function that takes a boolean. Ruby can’t know this
until it interprets the line, because you might have used eval() or
something to create that function before getting here.

In exchange for a lot more flexibility, Ruby does fewer sanity checks
at parse time.

To keep Ruby on track, and catch errors like this, all Ruby developers
should write unit tests for everything.

5

Austin Z. wrote:

"Greater than 0"
           * [email protected] * http://www.halostatue.ca/feed/
           * [email protected]

My word, you have just given me a reason to stop using returns !!!

It doesn’t hurt code readability to go by syntax rather then insert the
“Yes
Mr/Miss Programmer don’t forget we return here” return statements
through out
code ether.

TerryP.