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    <p>When you write an expression <code>c:Char =&gt; 1</code>, Scala compiler treats it as <code>c:(Char =&gt; 1)</code>, that is, a function variable <code>c</code> with type <code>Char =&gt; 1</code>. However, <code>1</code> is not a valid type (or type variable), so Scala compiler complains. So you need to write <code>s.toList map ((c:Char) =&gt; 1)</code> to help the compiler out of the type association.</p> <p><code>{c:Char =&gt; 1}</code> creates a function literal, that is, a function that accepts a char and returns 1. So</p> <pre><code>s.toList map {c:Char =&gt; 1} </code></pre> <p>is the same as</p> <pre><code>s.toList map({c:Char =&gt; 1}) // or val fn = {c: Char =&gt; 1} s.toList map fn </code></pre> <p><del>However, it seems that Scala doesn't have special specification for the <code>{c:Char =&gt; blabla}</code> form for creating function literals. </del></p> <p><del>I think it is because that there is <code>{some_var: SomeType =&gt; *Class Definition* }</code> form in class definition to reference <code>this</code> with <code>some_var</code> and add lower bound of the type of <code>this</code>. This causes the Scala lexer to treat a single typed parameter after <code>{</code> to be formal parameter and treat the statements after <code>=&gt;</code> to be actual body. Note that you <strong><em>CANNOT</em></strong> create a function with 2 parameters like this <code>{c: Char, d:Char =&gt; 1}</code>.</del></p> <p><strong>UPDATE</strong>: As commented by <em>som-snytt</em>, it is result expression that causes the brace version to be evaluated to a function result.</p>
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    1. POScala compiler says "error: identifier expected but integer literal found." for () not {}
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    1. COI can see why you speculate about the braces as you do, but it's actually not hard to look at the spec, cf my answer.
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    2. COYour opening statement is still misleading or imprecise. (Do I need parens? Are braces part of anon function syntax?) Probably the best suggestion is just to lose the type because it's inferred. In fact, http://docs.scala-lang.org/style/types.html#function_values
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