Ruby syntax question

ruby-talk
1

Hi,

While debugging some ruby-code, I found a mis-typed construct like the
following,
which looks like a syntax error to me,
but when you run it in irb it evaluates to nil and does NOT raise an
error:

x = def
puts xyz
end

(where xyz is undefined)
Anyone can explain what the above code means to ruby?

In contrast, this code DOES raise a syntax error:

x = def
puts "xyz"
end

My versions is:
irb 0.9.5(05/04/13)
ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-mswin32]

TIA,
--------------------------- grz01

2

I believe that it is being interpreted as defining an empty method
like so:

def puts(xyz)
end

and assigning to x the result of the call to "def".

···

On Feb 4, 4:01 pm, "gr...@spray.se" <gr...@spray.se> wrote:

Hi,

While debugging some ruby-code, I found a mis-typed construct like the
following,
which looks like a syntax error to me,
but when you run it in irb it evaluates to nil and does NOT raise an
error:

x = def
puts xyz
end

(where xyz is undefined)
Anyone can explain what the above code means to ruby?

3

Alle Monday 04 February 2008, grz01@spray.se ha scritto:

Hi,

While debugging some ruby-code, I found a mis-typed construct like the
following,
which looks like a syntax error to me,
but when you run it in irb it evaluates to nil and does NOT raise an
error:

x = def
puts xyz
end

(where xyz is undefined)
Anyone can explain what the above code means to ruby?

In contrast, this code DOES raise a syntax error:

x = def
puts "xyz"
end

My versions is:
irb 0.9.5(05/04/13)
ruby 1.8.6 (2007-03-13 patchlevel 0) [i386-mswin32]

TIA,
--------------------------- grz01

I'm not sure, but I think ruby, seeing a newline after a def, expects the
statement to go on on the following line, just as when you write

1+2+
3

or

my_method(a, b,
c)

The first piece of code would be translated into

x = def puts xyz
end

that is to the definition of a method called puts which takes one parameter,
named xyz (the x= part plays no role in this matter).

In the second case, ruby tries to do the same, but finds a string where it
would expect the argument name, so throws an exception.

Stefano

4

Yup:

504 % echo "x = def
puts xyz
end
" | parse_tree_show
-:2: warning: void value expression
s(:lasgn, :x, s(:defn, :puts, s(:scope, s(:block, s(:args, :xyz), s(:nil)))))

···

On Feb 4, 2008, at 13:19 , Karl von Laudermann wrote:

On Feb 4, 4:01 pm, "gr...@spray.se" <gr...@spray.se> wrote:

Hi,

While debugging some ruby-code, I found a mis-typed construct like the
following,
which looks like a syntax error to me,
but when you run it in irb it evaluates to nil and does NOT raise an
error:

x = def
puts xyz
end

(where xyz is undefined)
Anyone can explain what the above code means to ruby?

I believe that it is being interpreted as defining an empty method
like so:

def puts(xyz)
end

and assigning to x the result of the call to "def".

5

Thanks for help guys.
Yes, makes sense.

/grz01

···

On Feb 4, 10:18 pm, Karl von Laudermann <doodpa...@mailinator.com> wrote:

On Feb 4, 4:01 pm, "gr...@spray.se" <gr...@spray.se> wrote:

> Hi,

> While debugging some ruby-code, I found a mis-typed construct like the
> following,
> which looks like a syntax error to me,
> but when you run it in irb it evaluates to nil and does NOT raise an
> error:

> x = def
> puts xyz
> end

> (where xyz is undefined)
> Anyone can explain what the above code means to ruby?

I believe that it is being interpreted as defining an empty method
like so:

def puts(xyz)
end

and assigning to x the result of the call to "def".