Scala Syntax Specification mismatch if-else with one line expression end by semicolon? - scala

Question

I'm learning Scala Syntax Specification.
Confused by the if-else syntax:
Expr1 ::= ‘if’ ‘(’ Expr ‘)’ {nl} Expr [[semi] ‘else’ Expr]
| ...
How could it match below if-else with one line expression end by semicolon ?
if (true) // \n
println(1); //\n
else //\n
println(2); //\n
Notice there're 4 lines and each followed by a '\n'. I have these questions:
When the 1st ; after println(1) match semi before else( [[semi] ‘else’ Expr] ), how to match the 2nd '\n' after ; after println(1) ?
How to match the 3rd '\n' after else ?
How to match the 2nd ; and the 4th '\n' after println(2) ? Since if-else don't match any ; or '\n' at tail.

Answer 1

I think you are being confused by thinking that all newlines must match the nl token. That is not correct.
Newlines are in general simply treated as whitespace. There is a very long subsection on newlines in the Lexical Syntax chapter section 1.2 Newline characters which explains in detail, when, exactly, a newline character is an nl token and when it isn't.
Only the first newline character in your example is an nl token, the other three are just whitespace.

Answer 2

in Scala, semicolon ; doesn't exist (is ignored)
if-else statement is so simple with brackets as :
if (true) {
"\n" // this will be returned
println(1) // this will be ignored
"\n" // this will be ignored
} else {
"\n" // this will be returned
println(2) // this will be ignored
"\n" // this will be ignored
}
or, you can use without accolades, but the statement must be writed in one line:
if (true)
"\n" // this will be returned, can not have another line here
else
"\n"
without comments: if (true) "\n" else "\n"
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