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Document labeled break and continue in the reference manual

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r=brson
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Tim Chevalier 2012-10-26 14:05:21 -07:00
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doc/rust.md
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@ -1951,32 +1951,48 @@ while i < 10 {
### Infinite loops
A `loop` expression denotes an infinite loop:
The keyword `loop` in Rust appears both in _loop expressions_ and in _continue expressions_.
A loop expression denotes an infinite loop;
see [Continue expressions](#continue-expressions) for continue expressions.
~~~~~~~~{.ebnf .gram}
loop_expr : "loop" '{' block '}';
loop_expr : "loop" [ ident ':' ] '{' block '}';
~~~~~~~~
A `loop` expression may optionally have a _label_.
If a label is present,
then labeled `break` and `loop` expressions nested within this loop may exit out of this loop or return control to its head.
See [Break expressions](#break-expressions).
### Break expressions
~~~~~~~~{.ebnf .gram}
break_expr : "break" ;
break_expr : "break" [ ident ];
~~~~~~~~
Executing a `break` expression immediately terminates the innermost loop
enclosing it. It is only permitted in the body of a loop.
A `break` expression has an optional `label`.
If the label is absent, then executing a `break` expression immediately terminates the innermost loop enclosing it.
It is only permitted in the body of a loop.
If the label is present, then `break foo` terminates the loop with label `foo`,
which need not be the innermost label enclosing the `break` expression,
but must enclose it.
### Loop expressions
### Continue expressions
~~~~~~~~{.ebnf .gram}
loop_expr : "loop" ;
continue_expr : "loop" [ ident ];
~~~~~~~~
Evaluating a `loop` expression immediately terminates the current iteration of
the innermost loop enclosing it, returning control to the loop *head*. In the
case of a `while` loop, the head is the conditional expression controlling the
loop. In the case of a `for` loop, the head is the call-expression controlling
the loop.
A continue expression, written `loop`, also has an optional `label`.
If the label is absent,
then executing a `loop` expression immediately terminates the current iteration of the innermost loop enclosing it,
returning control to the loop *head*.
In the case of a `while` loop,
the head is the conditional expression controlling the loop.
In the case of a `for` loop, the head is the call-expression controlling the loop.
If the label is present, then `loop foo` returns control to the head of the loop with label `foo`,
which need not be the innermost label enclosing the `break` expression,
but must enclose it.
A `loop` expression is only permitted in the body of a loop.