Ruby newbie newline question

[Gary McGath]

I'm an experienced programmer but a complete beginner at Ruby.

I've tried to find an explanation of how newlines affect Ruby syntax,
without success. Some websites claim that Ruby doesn't care about
newlines, which is clearly false.

The following code works:

if i == 1
print "one"
elsif i == 2
print "two"
end

If I put the same code all on one line, it gets an error ("unexpected
kELSIF, expecting $end"). But if I add "then"s, i.e.,

if i == 1 then print "one" elsif i == 2 then print "two" end

then it works.

Could someone explain just what newlines do in cases like these, or at
least provide some guidelines to when I need them?

 

[Robert Klemme]

I'm an experienced programmer but a complete beginner at Ruby.

I've tried to find an explanation of how newlines affect Ruby syntax,
without success. Some websites claim that Ruby doesn't care about
newlines, which is clearly false.

The following code works:

if i == 1
print "one"
elsif i == 2
print "two"
end

If I put the same code all on one line, it gets an error ("unexpected
kELSIF, expecting $end"). But if I add "then"s, i.e.,

if i == 1 then print "one" elsif i == 2 then print "two" end

then it works.

There's also ";" which can be used instead:

$ ruby19 -ce 'if i == 1 then print "one" elsif i == 2 then print "two" end'
Syntax OK
$ ruby19 -ce 'if i == 1; print "one" elsif i == 2 then print "two" end'
Syntax OK
$ ruby19 -ce 'if i == 1 print "one" elsif i == 2 then print "two" end'
-e:1: syntax error, unexpected tIDENTIFIER, expecting keyword_then or
';' or '\n'
if i == 1 print "one" elsif i == 2 then print "two" end
^
-e:1: syntax error, unexpected keyword_elsif, expecting $end
if i == 1 print "one" elsif i == 2 then print "two" end
^

Note: all on 1 line each.

Could someone explain just what newlines do in cases like these, or at
least provide some guidelines to when I need them?

Basically you need to separate individual statements. You can do that
with a line terminator or with semicolon. "end" does not need a
separator before it because it is a keyword - unless you want to define
a class:

$ ruby19 -ce 'class X end'
-e:1: syntax error, unexpected keyword_end, expecting '<' or ';' or '\n'
-e:1: syntax error, unexpected $end
$ ruby19 -ce 'class X; end'
Syntax OK
$

I'm afraid I do not have more advice here. But this was really never a
big issue for me IIRC. Just code away and let the syntax check give
your the feedback.

Kind regards

robert

 

[Gary McGath]

There's also ";" which can be used instead:

$ ruby19 -ce 'if i == 1 then print "one" elsif i == 2 then print "two" end'
Syntax OK
$ ruby19 -ce 'if i == 1; print "one" elsif i == 2 then print "two" end'
Syntax OK
$ ruby19 -ce 'if i == 1 print "one" elsif i == 2 then print "two" end'
-e:1: syntax error, unexpected tIDENTIFIER, expecting keyword_then or
';' or '\n'
if i == 1 print "one" elsif i == 2 then print "two" end
^
-e:1: syntax error, unexpected keyword_elsif, expecting $end
if i == 1 print "one" elsif i == 2 then print "two" end
^

I see. Semicolon is a statement terminator, rather than being an
assignment terminator as in C-family languages. Useful to know.

I'm afraid I do not have more advice here. But this was really never a
big issue for me IIRC. Just code away and let the syntax check give
your the feedback.

Making conservative assumptions rather than trying to pare the code to
the minimum number of characters also sounds like good advice (i.e.,
Ruby is not Perl .

I've been using _Learning Ruby_ from O'Reilly, which is readable but not
nearly as precise as I'd like. Thanks for the input.

 

[Robert Klemme]

I see. Semicolon is a statement terminator, rather than being an
assignment terminator as in C-family languages. Useful to know.


Making conservative assumptions rather than trying to pare the code to
the minimum number of characters also sounds like good advice (i.e.,
Ruby is not Perl .

And that's good - definitively!

I've been using _Learning Ruby_ from O'Reilly, which is readable but not
nearly as precise as I'd like. Thanks for the input.

Well, actually Ruby's syntax is quite flexible - maybe too flexible in
some places. But it's great that you can omit brackets for methods
arguments. That makes creating DSLs pretty easy. Actually some things
which look like keywords are actually methods:

irb(main):001:0> Class.instance_method :attr_reader
=> #<UnboundMethod: Class(Module)#attr_reader>
irb(main):002:0> class Foo; method :attr_reader; end
=> #<Method: Class(Module)#attr_reader>

Kind regards

robert