This is probably my favorite explanation of HM type inference, based on an analogy with region-based memory management: <a href="http:&#x2F;&#x2F;okmij.org&#x2F;ftp&#x2F;ML&#x2F;generalization.html" rel="nofollow">http:&#x2F;&#x2F;okmij.org&#x2F;ftp&#x2F;ML&#x2F;generalization.html</a>