Confusion between precedence of unary minus and puts method

Ruby
1

If I write

puts 10 - 5

gives 5, same as

puts(10 -5)

Now if I write

puts(- 5)
#gives -5
But if I try -
puts - 5
#NoMethodError: undefined method `-’ for nil:NilClass

It seems, puts - 5 is parsed as (puts) - 5.

But why not are we allowed to write the unary operation with puts
like we are allowed with binary one ?

Regards,
Arup R.

2

Use:

puts -5
3

The topic was already discussed here
https://www.ruby-forum.com/topic/207933

The parser needs to decide whether an operator is binary or unary. As it
not yet incorporates A.I. conditions have to be unambiguous and space
before an argument (or lack of it) helps parser in decision. Enclosing
in parentheses enforces associativity so an extra space is ignored.

4

On Mon, Jul 28, 2014 at 9:34 AM, Arup R.
[email protected] wrote:

But if I try -
puts - 5

NoMethodError: undefined method `-’ for nil:NilClass

It seems, puts - 5 is parsed as (puts) - 5.

But why not are we allowed to write the unary operation with puts like
we are allowed with binary one ?

Because the parser needs a way to make a decision about ambiguous
syntax to remove ambiguity. The expression “puts - 5” parses the same
as “expr1 - expr2”, i.e. a binary minus expression. There is really no
other way to interpret that without sacrificing consistency.

Kind regards

robert