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POIs there a programming language that allows variable declaration at call site?
 

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  1. POIs there a programming language that allows variable declaration at call site?
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    <p><strong>Update 2:</strong> examples removed, because they were misleading. The ones below are more relevant.</p> <p>My question: </p> <p>Is there a programming language with such a construct?</p> <p><strong>Update:</strong> Now when I think about it, Prolog has something similar. I even allows defining operations at definition line. (forget about backtracking and relations - think about syntax)</p> <p>I asked this question because I believe, it's a nice thing to have symmetry in a language. Symmetry between "in" parameters and "out" parameters.</p> <p>If returning values like that would be easy, we could drop explicit returning in designed language.</p> <p>retruning pairs ... I think this is a hack. we do not need <em>a data structure</em> to pass multiple parameters to a function.</p> <p><strong>Update 2:</strong></p> <p>To give an example of syntax I'm looking for:</p> <pre><code>f (s, d&amp;) = // &amp; indicates 'out' variable d = s+s. main = f("say twice", &amp;twice) // &amp; indicates 'out' variable declaration print(twice) main2 = print (f("say twice", _)) </code></pre> <p>Or in functional + prolog style</p> <pre><code>f $s (s+s). // use $ to mark that s will get it's value in other part of the code main = f "say twice" $twice // on call site the second parameter will get it's value from print twice main2 = print (f "Say twice" $_) // anonymous variable </code></pre> <p>In a proposed language, there are no expressions, because all returns are through parameters. This would be cumbersome in situations where deep hierarchical function calls are natural. Lisp'ish example:</p> <pre><code>(let x (* (+ 1 2) (+ 3 4))) // equivalent to C x = ((1 + 2) * (3 + 4)) </code></pre> <p>would need in the language names for all temporary variables:</p> <pre><code>+ 1 2 res1 + 3 4 res2 * res1 res2 x </code></pre> <p>So I propose anonymous variables that turn a whole function call into value of this variable:</p> <pre><code>* (+ 1 2 _) (+ 3 4 _) </code></pre> <p>This is not very natural, because all the cultural baggage we have, but I want to <em>throw away</em> all preconceptions about syntax we currently have.</p>
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    1. COI believe this should be wiki...
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    2. COAnyway, is there a real *need* for this?
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    3. COIs there a reason for that?
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