1.3. Statement terminator
Important
rok statements end with a semicolon (;). A line break alone cannot end a statement.
stmt_terminator ::= ";"
1.3.1. Rules
The statement terminator follows a few simple rules. A statement ends with exactly one ;, and several statements may share one line. A statement may also span several lines, because a line break is merely whitespace between tokens.
Schematically:
<stmt> ;
<stmt> ; <stmt> ; // several on one line
<part of a stmt
spanning lines> ; // multiple lines. ends at the final ;
1.3.2. Why there is no automatic insertion at line breaks
rok does not adopt automatic rules such as JavaScript's ASI (Automatic Semicolon Insertion), Go's automatic end-of-line semicolons, or Swift's line-based termination.
The reasons are as follows. First, automatic rules create ambiguity in rare cases; JavaScript's ASI pitfalls are a well-known example. Second, an explicit terminator lets tools such as formatters, LSPs and editors' jump-to-next-statement determine statement boundaries deterministically. Finally, writing several statements on one line is natural in places such as quick REPL input.
1.3.3. Empty statements
An empty statement consisting only of ; is allowed and has no effect.
;;;
The code above is recognized as three empty statements. This form is accepted to give tool-generated code more freedom.
1.3.4. Block-like expression statements
When a block-like expression ending in } - if, match, loop, while, for, or a block ({ }, unsafe { }, labeled block) - appears in statement position, the trailing ; may be omitted (the same rule as Rust). The value of that expression must then be unit; to discard a non-unit value, add ;.
A call with a block-body trailing closure (retry(3) { .. }, xs.each |x| { .. }) also ends a statement without ; (4.8.8). In that case the call's value is discarded as if ; had been written.
if ready { start(); } // no ;
for x in xs { print(x); }
let n = if a { 1 } else { 2 }; // a let statement still ends with ;
If a binary operator follows the } of a block-like expression statement that starts with a keyword (if, match, etc.), it begins a new statement. Only member access such as .method() and postfix ? continue the expression. A binary operator after a trailing closure call is parsed as continuing that call.
if c { a(); } else { b(); }
-x; // new statement (not the if statement minus x)
match v { ... }.len(); // . continues
A non-block-like expression appearing as a statement in the middle of a block requires ;. Only the last expression of a block (the block's value) may appear without ;.
The grammar is defined by stmt in Block expressions.
1.3.5. Adjacency with other tokens
The ; token may be attached to the tokens before and after it without whitespace. For example, <stmt>;<stmt>; written without gaps still tokenizes correctly as two statements. Spacing for readability is the recommended style, but the specification itself does not enforce style.