I am writing a type inference engine for a simple ML-like language, and I am wondering how to infer the variance of type parameters. I know a little about variance already, so I could figure it out for some basic cases, like in type
<br><br>&nbsp;&nbsp;&nbsp; type (&#39;a, &#39;b) funct = &#39;a -&gt; &#39;b<br><br>the type variable &#39;a is contravariant, and &#39;b is covariant, and in case one variable would be co- and contravariant at the same time, it is invariant
<br><br>&nbsp;&nbsp;&nbsp; type (&#39;a, &#39;b) both &nbsp; = &nbsp; Left of &#39;a -&gt; &#39;b&nbsp;&nbsp; | &nbsp; Right of &#39;b -&gt; &#39;a.<br><br>But I have no idea on how to compute variance of complex types, like<br><br>&nbsp;&nbsp;&nbsp; type (&#39;a, &#39;b, &#39;c) long_funct = (&#39;a -&gt; &#39;b) -&gt; &#39;c
<br><br>since the whole (&#39;a -&gt; &#39;b) is in contravariant position, so &#39;a is twice contravariant, and b is first contra-, and the covariant.<br><br>Any resources?<br>