There's no meaningful whitespace in your example. You have a syntax error in the first example.

To get the effect you wanted in the you needed a `.`:

  1> 2 + 2
  1> .
  4

That is, if you really wanted it split over multiple lines.

The syntax error is indicated as being on line 2 (though not obviously on line 2) with the prefix to the error:

  * <line number>: <syntax error information>

What you've essentially typed in your first example is (replacing the newline with a single space):

  1> 2 + 2 2 + 2.

You'd expect an error from that since there is no operator between the second and third 2. Even placing a comma would've been enough:

  1> 2 + 2
  1> ,2 + 2. ;; this is weird to do, but valid
  4

The shell expects a period terminating an expression before it parses it. This permits entering multi-line expressions without doing anything special (you don't need a special "I'm going to continue on to the next line please don't parse this one" backslash, for instance).