 <p>I don't think there is a straightforward way to do this in general. You could probably use an <code>inline</code> operator with a mix of static member constraints to cover <em>some</em> of the cases that you want, but I don't think it will be very elegant.</p> <p>For some operator names, you can however define a separate <em>prefix</em> and <em>infix</em> version, which covers the first two cases:</p> <pre><code>// Prefix version of the operator (when you write e.g. '+. 10') let (~+.) a = a * 10 // Infix version of the operator (when you write e.g. '1 +. 10') let (+.) a b = a + b // Sample use +. 10 10 +. 20 </code></pre> <p>You still won't be able to write <code>10 +. 20 30 40</code>, because then you'd need an overloaded infix operator. </p> <p>It is worth noting that you cannot do this for all operator names. Here is a syntax definition from the <a href="http://fsharp.org/about/files/spec.pdf" rel="nofollow">F# specification</a> of the allowed operator names for infix operators:</p> <blockquote> <p>infix-or-prefix-op :=<br> &#160; &#160; &#160; +, -, +., -., %, &amp;, &amp;&amp;</p> <p>prefix-op :=<br> &#160; &#160; &#160; infix-or-prefix-op<br> &#160; &#160; &#160; ~ ~~ ~~~ (and any repetitions of ~)<br> &#160; &#160; &#160; !OP (except !=)</p> </blockquote> <p>PS: I'm not generally a big fan of custom operators - in some cases, they are nice, but they are difficult to discover (you do not see them in the IntelliSense) and unless you're using standard ones for numerical computing, it is often difficult to understand what they mean. So I would maybe consider other approaches...</p>