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POSince functions are first-class values in F#, why can't I use lambdas as values?
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copied!<p>If I define a simple function:</p> <pre><code>let myConcat a b = a + "+" + b </code></pre> <p>Then given the claim that functions are first-class values in F#, I'd expect to be able to use <code>myConcat</code> like this:</p> <pre><code>let result = myConcat "a" (fun () -> "b") </code></pre> <p>Rather than yielding a string "a+b", it gives me the following error:</p> <pre><code>error FS0002: This function takes too many arguments, or is used in a context where a function is not expected </code></pre> <p>Hopefully, I'm simply getting the syntax wrong, but it looks to me like functions cannot truly be used as values in F#. Can anyone explain what's going on here?</p> <p><strong>EDIT</strong> To further clarify what I'm asking, I could have the equivalent C# code:</p> <pre><code>public string myConcat(string a, string b) { return a + "+" + b; } </code></pre> <p>If I however wanted to pass a "call later function" in param b, I'd have to make it:</p> <pre><code>public string myConcat(string a, Action<string> b) { return a + "+" + b(); } </code></pre> <p>Or I could call it thus:</p> <pre><code>Func<string> b = () => "b"; var result = myConcat("a", b()); </code></pre> <p>C# doesn't (to my knowledge) make the claim that functions are first-class values. F# does make that claim. So what's the difference when I can't treat a unit -> string function as a "lazy evaluated" string value?</p>

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