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rename expr-anon-closure -> expr-explicit-closure.

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Change the wording to claim that $0 is only valid in an explicit
closure.  Add a note about possibly generalizing closure syntax in the future.


Swift SVN r1155
This commit is contained in:
Chris Lattner
2012-03-04 04:33:58 +00:00
parent 6aac93155d
commit f13a615e78
1 changed files with 23 additions and 12 deletions
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35
docs/LangRef.html
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@@ -1383,7 +1383,7 @@
expr-primary ::= <a href="#expr-literal">expr-literal</a>
expr-primary ::= <a href="#expr-identifier">expr-identifier</a>
expr-primary ::= <a href="#expr-anon-closure">expr-anon-closure</a>
expr-primary ::= <a href="#expr-explicit-closure">expr-explicit-closure</a>
expr-primary ::= <a href="#expr-anon-closure-arg">expr-anon-closure-arg</a>
expr-primary ::= <a href="#expr-paren">expr-paren</a>
expr-primary ::= <a href="#expr-delayed-identifier">expr-delayed-identifier</a>
@@ -1507,11 +1507,21 @@
href="decl-func">func</a> declarations.</p>
<!-- ===================================================================== -->
<h3 id="expr-anon-closure">Anonymous Closure Expression</h3>
<h3 id="expr-explicit-closure">Explicit Closure Expression</h3>
<!-- ===================================================================== -->
<div class="commentary">
It would be possible to allow { expr } and { stmt-brace-item* } here -
allowing the same syntax as stmt-brace. The
intepretation of this would be that a single expression is evaluated and
returned implicitly, but that a multi-statement sequence would require an
explicit return. This would mean that {4} and {return 4} both do the same
thing. OTOH, it is possibly confusing that {4} and {4;} would have very
different meanings.
</div>
<pre class="grammar">
expr-anon-closure ::= '{' expr '}'
expr-explicit-closure ::= '{' expr '}'
</pre>
<p>A closure expression is a super-concise version of <a
@@ -1526,7 +1536,7 @@
<p>It is illegal to use these expressions when there is insufficient context
to infer the argument and return types of the closure.</p>
<p>Note that expr-anon-closure is ambiguous with <a
<p>Note that expr-explicit-closure is ambiguous with <a
href="#stmt-brace">stmt-brace</a> when used in a another stmt-brace or in
<a href="#decl-translation-unit">translation-unit</a> scope. This
ambiguity is resolved towards stmt-brace, because these context never have
@@ -1534,16 +1544,19 @@
would always be a semantic error if parsed that way.</p>
<pre class="example">
// Takes a closure that it calls to determine an ordering relation.
<i>// Takes a closure that it calls to determine an ordering relation.</i>
func magic(val : int, predicate : (a : int, b : int) -> bool)
func f() {
// Compare one way.
<i>// Compare one way. Closure is inferred to return bool and take two ints</i>
<i>// from the argument context. This same information infers that $0 and $1</i>
<i>// both have type 'int'.</i>
magic(42, { $0 &lt; $1 })
// Compare the other way way.
<i>// Compare the other way way.</i>
magic(42, { $1 &lt; $0 })
// Error, not enough context to infer the type of $0.
<i>// Error, not enough context to infer the type of $0.</i>
var x = { $0 }
}
</pre>
@@ -1561,10 +1574,8 @@
the containing expression is <a href="#typecheck_anon">coerced into a closure
context</a>. All other dollar identifiers are invalid.</p>
<p>This is typically used in the body of an <a
href="#expr-anon-closure">expr-anon-closure</a> but can also be used when
autoclosing an expression to a closure type.
FIXME: Nail this down and add support for it.
<p>This can only be used in the body of an <a
href="#expr-explicit-closure">expr-explicit-closure</a>.
</p>