Another really helpful resource to understand algorithm W inferring types for HM is Algorithm-W-Step-by-Step at [1].<p>[1]. <a href="http:&#x2F;&#x2F;citeseerx.ist.psu.edu&#x2F;viewdoc&#x2F;download?doi=10.1.1.65.7733&amp;rep=rep1&amp;type=pdf" rel="nofollow">http:&#x2F;&#x2F;citeseerx.ist.psu.edu&#x2F;viewdoc&#x2F;download?doi=10.1.1.65....</a>