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copied!<p>Thanks for this question - it is a really nice bug report with a simple repro and I couldn't believe this, but you're completely right. Plus works, but minus doesn't.</p> <p><strong>The problem</strong> is that <code>sub</code> and <code>add</code> are compiled as generic methods and the LINQ version invokes these generic methods. The inlining is performed <em>after</em> quotations are stored, so the quoted code contains call to the <code>sub</code> method. This isn't a problem in normal F# code, because the functions are inlined and the operators are resolved to + or - over some numeric types.</p> <p>However, the generic version uses a dynamic lookup. If you look into <code>prim-types.fs:3530</code>, you'll see:</p> <pre><code>let inline (+) (x: ^T) (y: ^U) : ^V = AdditionDynamic<(^T),(^U),(^V)> x y when ^T : int32 and ^U : int32 = (# "add" x y : int32 #) when ^T : float and ^U : float = (# "add" x y : float #) // ... lots of other cases </code></pre> <p>The <code>AdditionDynamic</code> is what gets called from the generic method. It does the dynamic lookup, which will be slower, but it will work. Interestingly, for the minus operator, the F# library doesn't include dynamic implementation:</p> <pre><code>[<NoDynamicInvocation>] let inline (-) (x: ^T) (y: ^U) : ^V = ((^T or ^U): (static member (-) : ^T * ^U -> ^V) (x,y)) when ^T : int32 and ^U : int32 = (# "sub" x y : int32 #) when ^T : float and ^U : float = (# "sub" x y : float #) // ... lots of other cases </code></pre> <p>I have no idea why this is the case - I don't think there is any technical reason, but it explains why you get the behavior you reported. If you look at the compiled code using ILSpy, you'll see that the <code>add</code> method does something and the <code>sub</code> method just throws (so this is where the exception comes from).</p> <p><strong>As for a workaround</strong>, you need to write the code in a way in which it doesn't use the generic minus operator. Probably the best option is to avoid <code>inline</code> functions (either by using <code>sub_int</code> or <code>sub_float</code>) or by writing your own dynamic implementation of <code>sub</code> (which can be done probably quite efficiently using DLR (see <a href="https://stackoverflow.com/questions/689240/how-is-the-upcoming-dynamic-keyword-in-net-4-0-going-to-make-my-life-better">this post</a>).</p>

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