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Simplify loop by removing second label #710

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Simplify loop by removing second label #710

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460938b
Simplify loop by removing its exit label.
sunfishcode Jun 17, 2016
1c0697e
Remove "either".
sunfishcode Sep 14, 2016
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11 changes: 7 additions & 4 deletions AstSemantics.md
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Expand Up @@ -345,9 +345,12 @@ a value and may appear as children of other expressions.
### Branches and nesting

The `br` and `br_if` constructs express low-level branching.
Branches may only reference labels defined by an outer *enclosing construct*.
This means that, for example, references to a `block`'s label can only occur
within the `block`'s body.
Branches may only reference labels defined by an outer *enclosing construct*,
which can be a `block` (with a label at the `end`), `loop` (with a label at the
beginning), `if` (with a label at the `end` or `else`), `else` (with a label at
the `end), or the function body (with a label at the `end`). This means that,
for example, references to a `block`'s label can only occur within the
`block`'s body.

In practice, outer `block`s can be used to place labels for any given branching
pattern, except for one restriction: one can't branch into the middle of a loop
Expand All @@ -367,7 +370,7 @@ The `nop`, `br`, `br_if`, `br_table`, and `return` constructs do not yield value
Other control constructs may yield values if their subexpressions yield values:

* `block`: yields either the value of the last expression in the block or the result of an inner branch that targeted the label of the block
* `loop`: yields either the value of the last expression in the loop or the result of an inner branch that targeted the end label of the loop
* `loop`: yields the value of the last expression in the loop
* `if`: yields either the value of the last *then* expression or the last *else* expression or the result of an inner branch that targeted the label of one of these.

In all constructs containing block-like sequences of expressions, all expressions but the last must not yield a value.
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