From: Colin Bartlett <colinb2r@...>
Date: 2011-01-18T04:03:41+09:00
Subject: Re: Obscure syntax error

On Mon, Jan 17, 2011 at 12:39 PM, Rolf Timmermans <molfie@gmail.com> wrote:
> ...
> Exactly. And to be entirely clear, the fact that the method does not exist doesn't even matter.
> If the method does exist, the same syntax error is raised if the first argument is a symbol.
> And when using parentheses, no syntax error occurs
> ...
> def x(*args); end
> x :y
> # No error
>
> def x(*args); end
> x = nil
> x :y
> # foo.rb:3: syntax error, unexpected ':', expecting $end
>
> def x(*args); end
> x = nil
> x(:y)
> # No error

I don't have an explanation for why using the symbol gives a
SyntaxError rather than a NoMethodError, but the above three of your
new examples seem to me to be the key examples, together with maybe
the following on Ruby1.9.1. Note that using "eval" with x not being
defined as a variable also raises a SyntaxError.

## two types of error message:
##   NoMethodErr === #<NoMethodError: undefined method `x' for main:Object>
##   SyntaxErr   === #<SyntaxError: syntax error, unexpected ':', expecting ')'
y = nil
puts "** not eval; defined?( x ) #=> #{defined?( x ).inspect}"
(x :y) rescue (p $!)   # NoMethodErr
(x 'y') rescue (p $!)  # NoMethodErr
(x y) rescue (p $!)    # NoMethodErr

puts "** eval; defined?( x ) #=> #{defined?( x ).inspect}"
begin; eval "(x :y)"; rescue SyntaxError; p $!; end  # SyntaxErr
eval "(x 'y')" rescue (p $!)  # NoMethodErr
eval "(x y)" rescue (p $!)    # NoMethodErr